Chances are, if you're paying in cash, you might not even get things like a receipt, bank documentation, or even a title. Obviously, that's not good. This means you have no way to prove the car belongs to you, and if you try to be the good guy and turn it in, Johnny Law may have to put the cuffs on you. Always be sure to get some sort of paperwork that legally binds the vehicle to you and can be traced back to who you bought it from.