Don't consider this list comprehensive, but I'll try and help out:
1. Maintenance records...you want details
2. Drive test...does it ride smoothly? does the trans shift normally? Hit it hard going up a hill and see if it slips. Does the engine rev normally? You don't want hesitation or bogging
3. Check tires...look for uneven wear. That will tell you that they A) weren't maintained and B) there is probably alignment issues, again pointing toward neglect
4. Braking - should be smooth. No shuddering or pulling to one side.
5. Rust - check frame and body from the underside as well as topside.
6. Check underside for leaks.
7. Check oil. This can be tricky...fresh oil isn't always good. That can indicate that the P/O is trying to cover something up. If possible, capture a sample and send to Blackstone labs for analysis
8. Suspension - listen for creaks/groans/squeaks/pops etc. Inspect bushings, make sure nothing is broken or dry rotted. If you can, check for play in all joints and wheel hubs
