Lots of good advice above. I would suggest a meeting place nestled deep in a starbucks or panera bread or something like that. Form a checklist of what you need to test:
1. Condition of machine
2. Turning on computer
3. Screen
4. About this Mac
5. Check wireless
6. Check sound
7. Check superdrive
8. Change wallpaper backgrounds to check screen for spots/dead pixels
9. Check battery - install coconut battery if needed
10. Check Apple Care status from the serial from the about this mac
11. Check specs to make sure they match the offer
1. Condition of machine
2. Turning on computer
3. Screen
4. About this Mac
5. Check wireless
6. Check sound
7. Check superdrive
8. Change wallpaper backgrounds to check screen for spots/dead pixels
9. Check battery - install coconut battery if needed
10. Check Apple Care status from the serial from the about this mac
11. Check specs to make sure they match the offer