Prior damage. Look for nonstandard spot welds, inconsistent paint spray, or misaligned decals. Check door jambs beneath the rubber seals, beneath the trunk lining, and the rails in the engine bay. That’s not to say that a car which has had prior damage is never worth buying, but it’s information you’d want to know before making your decision.

Odometer fraud. Make sure all of the maintenance records match up, and that the accumulated mileage didn’t somehow decrease between services. Some cars have a tamper light or indicator; check and make sure that isn’t active. If you’re dealing with something that uses OBD-II, maybe get an inexpensive device to plug in and make sure the numbers match what’s on the instrument cluster—it’s a lot harder and costlier to trick the car’s internal systems into recording an incorrect figure. And make sure the wear of the car matches the mileage.