[Ian]

obviously check for any sort of leaks. rear tire wear. also check the wear pattern on the front tires. if one front tire is wearing out the outter or inner shoulder of the tire, chances are it needs an alignment. Hell, it could even mean they smacked a curb with it.

Drive it. make sure there arent any strange noises. make sure the trans shifts okay if its auto. make sure the clutch doesnt feel funny if its stick. also if its stick, be sure to see if the trans itself is shifting okay. If you have trouble going into any of the gears, it may have a messed up shifter or a bent shift fork.

drive in a straight line and let go of the wheel, make sure it doesnt pull to either side. If it seems to go to the right a little bit, it might just be the crown of the road making it do that. also, with your hands off the wheel, hit the brakes and make sure it doesnt pull to either side while braking. if it pulls to the left, a suspension component on the right side is messed up. same goes for if it pulls right. or it could be a braking problem.

like everyone else said, check the body for damage. different shades of paint usually means a repair of some sort.