9. Beware of the 'yo-yo.'
If you finance through a dealer, make sure the terms are final, not contingent or conditional, before you sign and drive away. All too often buyers are told days or weeks later that their monthly payments or the required down payment has been increased. It's sometimes known as a "yo-yo sale," Frank says. Among the general population it happens to about one in every 22 buyers, according to an April 2009 survey from the Center for Responsible Lending. Among buyers with bad credit it's one in nine.