First and foremost, locate the VIN number on any car you're trying to buy. Usually it's on the driver's side at the base of the windshield and dashboard or on the inside of the door. There are sites like Carfax (you know, the one with that sneaky Car Fox?) and the National Insurance Crime Bureau that let you check the history report of a vehicle to see if it's been reported as salvaged or stolen. But beware, sometimes thieves will even switch out the VIN from a similar vehicle. A number that looks like it's been tampered with or scratched is the biggest red flag you can find.