Clifford 50.7X security system.

Here's what I have compiled so far:

Check radiator fins If bent, possible sign of turbo upgrade
Check stock intake If loose, possible sign of aftermarket intake
Check oil
Check tires
Check for warped brakes
Ask what warranty repairs have been done
Check door hinges If unpainted, doors may have been replaced
Check vins on all doors

Add...
Engine analysis...if it fails don't buy it...lol.
Emisions test...if it fails, you can't register it and you will have work to do and sometimes it will never pass even if you do all the work, so this is an important one.
Safety inspection...check brakes/emergency brake, etc...also make sure all electrical components are working....heater/airconditioning/lights/signals/emergency signals/wipers/auto-pilot-(lol...brains gone blank and I can't remember the name).
Check antifreeze and all levels of fluids. Check for oil leaks, or any other kind of leaks.
Check wear pattern on tires...may mean problem with frame/wheel balancing/alignment.
Check interior and exterior for slight changes in colors of paint or plastics.
Check seat bolts to make sure they haven't been altered for height, etc.
Check gaps for equal length all the way down the length on (doors/hood)...may mean accident...check paint for different tones/mirror image. Check hinges of doors/hood, and check for paint that should not be on certain items like hoses/hinges, etc.
Ask for receits/maintenece records...last oil change, tune-up, belt changes, etc.
Check underneath car for rust, (leaks) etc.
Ask for warranties transferable to you.
Carfax
Test drive for as long as you can...check alignment/steering/clutch. Drive with windows open and closed to hear noises inside and out.
Have someone look at the exhaust as you start the car.

Will try to think of more as we go along...