I've used #10 before.
10. (In the U.S.): if you’re ever pursued for a debt, especially if you are taken to court over it, demand that they produce documentation verifying that you owe the debt and the amount. Quite often, they won’t be able to and the case will be dismissed. Most debt collectors aren’t the party you originally owed the money to but rather companies that purchase debts in bulk for pennies on the dollar. Very often, all they have on you is your name on a spreadsheet and they’re banking on the fact that you won’t contest it. It is important to note that this really only works if you haven’t started paying them. Once you start paying them, you are basically agreeing that you owe them money.