Before you buy, you might want to take the time to pop the pipe off and look up the exhaust port with a flashlight. It is a nice big port so you can view the cylinder condition (for flaking) reach in with a finger and try to rock the piston and view the piston side wall. A compression test is faster and easier but nothing like a "look". Get a 1996 or newer. They have the updated forks and shock. Also look at the condition of big ticket items, worn tires are cheap to replace but things like really bent rads can cost lots of $$.
Here's a partial list:
compression test
look at shock shaft for leaking oil
run finger over fork sliders for nicks.
rad condition.
spin wheels to see if bent
lift bike to see how loose rear linkages are
look for watery rust marks around swingarm pivots (bearings shot)
Same for steering head (although much cheaper to fix) with bike on stand try to pull fork bottoms toward you.
Cam.