0. For a car, what scams can be plotted with 0% financing vs rebate?
The car deal makes money 3 ways. If you pay in one lump payment. If the payment is greater than what they paid for the car, plus their expenses, they make a profit. They loan you the money. You make payments over months or years, if the total amount you pay is greater than what they paid for the car, plus their expenses, plus their finance expenses they make money. Of course the money takes years to come in, or they sell your loan to another business to get the money faster but in a smaller amount. You trade in a car and they sell it at a profit. Of course that new transaction could be a lump sum or a loan on the used car... They or course make money if you bring the car back for maintenance, or you buy lots of expensive dealer options. Some dealers wave two deals in front of you: get a 0% interest loan. These tend to be shorter 12 months vs 36,48,60 or even 72 months. The shorter length makes it harder for many to afford. If you can't swing the 12 large payments they offer you at x% loan for y years that keeps the payments in your budget. pay cash and get a rebate. If you take the rebate you can't get the 0% loan. If you take the 0% loan you can't get the rebate. The price you negotiate minus the rebate is enough to make a profit. The key is not letting them know which offer you are interested in. Don't even mention a trade in until the price of the new car has been finalized. Otherwise they will adjust the price, rebate, interest rate, length of loan,  and trade-in value to maximize their profit. The suggestion of running the numbers through a spreadsheet is a good one. If you get a loan for 2% from your bank/credit union for 3 years and the rebate from the dealer, it will cost less in total than the 0% loan from the dealer. The key is to get the loan approved by the bank/credit union before meeting with the dealer. The money from the bank looks like cash to the dealer.

1. Why does it matter if a Central Bank has a negative rather than 0% interest rate?
That is kind of the point, one of the hopes is that it incentivizes banks to stop storing money and start injecting it into the economy themselves. Compared to the European Central Bank investing directly into the economy the way the US central bank has been doing. (The Federal Reserve buying mortgage backed securities) On a country level, individual European countries have tried this before in recent times with no noticeable effect.

2. Where should I be investing my money?
Pay off your debt.  As you witnessed, no "investment" % is guaranteed.  But your debt payments are... so if you have cash, the best way to "invest" it is to pay off your debt.  Since your car is depreciating while your house may be appreciating (don't know but it's possible) you should pay off your car loan first.  You're losing money in more than one way on that investment.

3. Specifically when do options expire?
Equity options, at least those traded in the American exchanges, actually expire the Saturday after the 3rd Friday of the month.  However, the choice to trade or exercise the options must be specified by the 3rd Friday. This is outlined by the CBOE, who oversees the exchange of equity options.  Their FAQ regarding option expiration can be found at http://www.cboe.com/LearnCenter/Concepts/Beyond/expiration.aspx.

4. Negative Balance from Automatic Options Exercise. What to do?
Automatic exercisions can be extremely risky, and the closer to the money the options are, the riskier their exercisions are. It is unlikely that the entire account has negative equity since a responsible broker would forcibly close all positions and pursue the holder for the balance of the debt to reduce solvency risk.  Since the broker has automatically exercised a near the money option, it's solvency policy is already risky. Regardless of whether there is negative equity or simply a liability, the least risky course of action is to sell enough of the underlying to satisfy the loan by closing all other positions if necessary as soon as possible. If there is a negative equity after trying to satisfy the loan, the account will need to be funded for the balance of the loan to pay for purchases of the underlying to fully satisfy the loan. Since the underlying can move in such a way to cause this loan to increase, the account should also be funded as soon as possible if necessary. Accounts after exercise For deep in the money exercised options, a call turns into a long underlying on margin while a put turns into a short underlying. The next decision should be based upon risk and position selection.  First, if the position is no longer attractive, it should be closed.  Since it's deep in the money, simply closing out the exposure to the underlying should extinguish the liability as cash is not marginable, so the cash received from the closing out of the position will repay any margin debt. If the position in the underlying is still attractive then the liability should be managed according to one's liability policy and of course to margin limits. In a margin account, closing the underlying positions on the same day as the exercise will only be considered a day trade.  If the positions are closed on any business day after the exercision, there will be no penalty or restriction. Cash option accounts While this is possible, many brokers force an upgrade to a margin account, and the ShareBuilder Options Account Agreement seems ambiguous, but their options trading page implies the upgrade. In a cash account, equities are not marginable, so any margin will trigger a margin call.  If the margin debt did not trigger a margin call then it is unlikely that it is a cash account as margin for any security in a cash account except for certain options trades is 100%. Equities are convertible to cash presumably at the bid, so during a call exercise, the exercisor or exercisor's broker pays cash for the underlying at the exercise price, and any deficit is financed with debt, thus underlying can be sold to satisfy that debt or be sold for cash as one normally would. To preempt a forced exercise as a call holder, one could short the underlying, but this will be more expensive, and since probably no broker allows shorting against the box because of its intended use to circumvent capital gains taxes by fraud.  The least expensive way to trade out of options positions is to close them themselves rather than take delivery.

5. Approximation of equity value for company in default
Generally "default" means that the company cannot pay off their debts, and since debt holders get paid before equity holders, their equity would be effectively worthless. That said, companies can emerge from Chapter 11 bankruptcy (reorganization) and retain equity value, but it is rare. Most times, stocks are de-listed or frozen on stock exchanges, and company's reorganization plan will cancel all existing equity shares, instead focusing all of their attention on paying back as much debt as possible. If the company issues new equity after reorganizing, it might provide a way for holders of the original equity to exchange their shares for the new equity, but it is rare, and the value is usually significantly less that the value of the original equity.

6. Is it true that 90% of investors lose their money?
The game is not zero sum. When a friend and I chop down a tree, and build a house from it, the house has value, far greater than the value of a standing tree. Our labor has turned into something of value.  In theory, a company starts from an idea, and offers either a good or service to create value. There are scams that make it seem like a Vegas casino. There are times a stock will trade for well above what it should. When I buy the S&P index at a fair price for 1000 (through an etf or fund) and years later it's 1400, the gain isn't out of someone else's pocket, else the amount of wealth in the world would be fixed and that's not the case. Over time, investors lag the market return for multiple reasons, trading costs, bad timing, etc. Statements such as "90% lose money" are hyperbole meant to separate you from your money. A self fulfilling prophesy.   The question of lagging the market is another story - I have no data to support my observation, but I'd imagine that well over 90% lag the broad market. A detailed explanation is too long for this forum, but simply put, there are trading costs. If I invest in an S&P ETF that costs .1% per year, I'll see a return of say 9.9% over decades if the market return is 10%. Over 40 years, this is 4364% compounded, vs the index 4526% compounded, a difference of less than 4% in final wealth. There are load funds that charge more than this just to buy in (5% anyone?).  Lagging by a small fraction is a far cry from 'losing money.'  There is an annual report by a company named Dalbar that tracks investor performance. For the 20 year period ending 12/31/10 the S&P returned 9.14% and Dalbar calculates the average investor had an average return of 3.83%. Pretty bad, but not zero. Since you don't cite a particular article or source, there may be more to the story. Day traders are likely to lose. As are a series of other types of traders in other markets, Forex for one.  While your question may be interesting, its premise of "many experts say...." without naming even one leaves room for doubt.  Note - I've updated the link for the 2015 report. And 4 years later, I see that when searching on that 90% statistic, the articles are about day traders. That actually makes sense to me.

7. Can a company charge you for services never requested or received?
In general, you can only be charged for services if there is some kind of contract. The contract doesn't have to be written, but you have to have agreed to it somehow. However, it is possible that you entered into a contract due to some clause in the home purchase contract or the contract with the home owners' association. There are also sometimes services you are legally required to get, such as regular inspection of heating furnaces (though I don't think this translates to automatic contracts). But in any case you would not be liable for services rendered before you entered into the contract, which sounds like it's the case here.

8. Working out if I should be registered as self-employed in the UK
Being self employed just means you fill out some more forms in your annual self assessment for your "profit" from being self employed.  Profit = all the money you receive, minus any tax deductible cost that you spent for making that money (and all the cost must be documented, which means you have a folder with all the receipts and keep it safe). You pay normal income tax on all the profit, which means it is just added to your taxable income. What you do with the profit is up to you; you don't pay yourself a salary, just take the money (make sure you leave enough to pay your taxes).

9. About eToro investments
For eToro, just like any other brokerage firm, you can lose your entire capital. I suggest that you invest in one or more exchange-traded funds that track major indexes.  If not, just put your money in fixed deposit accounts; gain a bit of interest and establish an emergency fund first before investing money that you feel you are able to lose.

10. Pay off car loan entirely or leave $1 until the end of the loan period?
Not sure if it is the same in the States as it is here in the UK (or possibly even depends on the lender) but if you have any amount outstanding on the loan then you wouldn't own the vehicle, the loan company would. This often offers extra protection if something goes wrong with the vehicle - a loan company talking to the manufacturer to get it resolved carries more weight than an individual. The laon company will have an army of lawyers (should it get that far) and a lot more resources to deal with anything, they may also throw in a courtesy car etc.

11. Including the region where you live in your investment portfolio?
Diversification is a risk-mitigation strategy. When you invest in equities, you generally get a higher rate of return than a fixed income investment. But you have risks... a single company's market value can decline for all sorts of reasons, including factors outside of the control of management. Diversification lets you spread risk and concentrate on sectors that you feel offer the best value. Investing outside of your currency zone allows you to diversify more, but also introduces currency risks, which require a whole other level of understanding. Today, investing in emerging markets is very popular for US investors because these economies are booming and US monetary policy has been weakening the dollar for some time. A major bank failure in China or a flip to a strong dollar policy could literally implode those investments overnight. At the end of the day, invest in what you understand. Know the factors that can lower your investment value.

12. Are there any rules against penalizing consumers for requesting accurate credit reporting?
The Fair Credit Reporting Act specifies in some detail on pages 50-54 (as labeled in the footer, 55-59 as pages in pdf) the process that occurs when a consumer initiates a dispute.  The safe outcome for the reporting agency is to remove the information in dispute  from reports within 30 days if the reporting party does not certify the information is complete and accurate (with other statutory timelines for communication to the customer and the reporter).   If you initiate a dispute, then the agency is following the law by deleting the reported information, outside new input from the furnisher.  If this is unsatisfactory, you have the following statutory right within § 611. Procedure in case of disputed accuracy [15 U.S.C. § 1681i (d) Notification of deletion of disputed information. Following any deletion of   information which is found to be inaccurate or whose accuracy can no longer   be verified or any notation as to disputed information, the consumer   reporting agency shall, at the request of the consumer, furnish notification   that the item has been deleted or the statement, codification or summary   pursuant to subsection (b) or (c) of this section to any person specifically   designated by the consumer who has within two years prior thereto received   a consumer report for employment purposes, or within six months   prior thereto received a consumer report for any other purpose, which   contained the deleted or disputed information.  The section that binds furnishers of information (§ 623. Responsibilities of furnishers of information to consumer reporting agencies [15 U.S.C. § 1681s-2], starting on page 78 in the footer) places on them the following specific duties: (B) Reporting information after notice and confirmation of errors.   A person shall not furnish information relating to a consumer to   any consumer reporting agency if   (i) the person has been notified by the consumer, at the address   specified by the person for such notices, that specific   information is inaccurate; and   (ii) the information is, in fact, inaccurate. ... (2) Duty to correct and update information. A person who   (A) regularly and in the ordinary course of business furnishes information   to one or more consumer reporting agencies about the   person’s transactions or experiences with any consumer; and   (B) has furnished to a consumer reporting agency information   that the person determines is not complete or accurate, shall   promptly notify the consumer reporting agency of that determination   and provide to the agency any corrections to that information,   or any additional information, that is necessary to make   the information provided by the person to the agency complete   and accurate, and shall not thereafter furnish to the agency any   of the information that remains not complete or accurate. So there you have it: they have to stop reporting inaccurate information, and "promptly" notify the credit agency once they've determined what is incomplete or inaccurate. I note no specific statutory timeline for this investigation.

13. What are the reasons to get more than one credit card?
Another good reason: if you have to replace a card due to damage, loss, or identity theft it's nice to have a backup you can use until the new card for your primary account arrives. I know folks who use a secondary card for online purchases specifically so they can kill it if necessary without impacting their other uses, online arguably being at more risk. If there's no yearly fee, and if you're already paying the bill in full every month, a second card/account is mostly harmless. If you have trouble restraining yourself with one card, a second could be dangerous.

14. Why is economic growth so important?
One of the best answers to this question that I've ever read is in a paper published by Robert Lucas in the Journal of Economic Perspectives. That journal is meant to a be a place for experts to write about their area of expertise (in economics) for a general but still technically-minded audience. They recently opened up the journal as free to the public, which is a fantastic resource -- you no longer need a subscription to JSTOR (or whatever) to read it.  You can read the abstract to the paper, and find a link to it, here. One of the things that I like a lot about this paper is that it strips out absolutely everything even slightly unnecessary to thinking about a macroeconomy, and just discusses what one can arrive at with a very very simple model. Of course, with great simplicity come sacrifice about details. However, it does a great job of answering your question, "why do people care about growth?" A quick note: the key to understanding the answer to your question is to think about things in terms of "the long term"  -- not even looking forward to the future, because we'll be dead by then, but looking back to the past. The key to the importance of growth is that, for the last ~200 years, the US has, on average, had maybe 2-3% "real growth" per year (I'm pulling these numbers out of my head; I think much better numbers are in that paper somewhere). On average, over that period of time, this growth has meant that the quality of life that one has, if one lives in a country experiencing this growth, is enormous compared to countries that do not experience this average growth over that period.  Statistically speaking, growth is also somewhat auto-correlated. Roughly speaking, if it was low the last few periods, you can expect it to be low the next period. Same thing if it's high.   Then, the reason we care about growth right now: if you have too many periods of low growth, pretty soon the average "over the long term" growth will be pulled down -- and then quality of life can't be higher in the future (which quickly becomes someone's "present"). The paper above makes this point with a very simple model. Of course, none of this touches on distributional issues, which are another issue entirely. With respect to, "The economy needs to grow to just keep up with its debt repayments," I think the answer is along the lines of, "sometimes countries get into debt expecting that growth will increase their resources in the future, and thus they can pay back their debt." That strategy is, of course, the strategy that anyone borrowing ("taking out a loan") should be employing -- you should expect that your future income will be enough to pay back your interest+principle on a loan you took. Otherwise you're irresponsible. At the aggregate level, production is the nation's "income" -- it is what you have, all that you have (as a nation) to pay back any debt you've incurred at the national level.

15. Investment strategy for retired couple
You need to have them consult with a financial adviser that has a focus on issues for seniors. This is because they are beyond the saving for retirement phase and are now in the making-their-money-last phase. They also have issues related to health insurance, IRA RMDs, long term care insurance. The adviser will need to review what they have and determine how to make sure it is what they need. It is great idea for you to go along with them so you can understand what needs to be done. You will want an adviser that charges you a fee for making the plan, not one that makes a commission based on what products you buy or invest in.

16. What is the US Fair Tax?
You asked about the challenges. The transition itself is the biggest one. For people to get used to the tax at the register vs at their paycheck. For a great number of people to find new work. I don't know the numbers, but anyone involved with personal income taxes would be out of work. Sales tax is already part of the process in most states, bumping it to a federal tax wont add too much in overhead.  I make no moral judgment, but consider, most prostitutes and drug dealers are avoiding income tax, but they still are buying the same goods in stores you and I are. This proposed tax reduces the collection noncompliance, and brings more people into "the system".  Another factor some may not like is the ability to affect behavior by picking and choosing what to promote, via deductions, such as home buying or charity.
