Listen for loud or strange engine noises when it running. When in neutral, rev it up quick and slow and see how it reacts. Check the bearring and ball jint on the front end, check rear bearings. Get it up on its back end and ckeck the frame for cracks (specially right in front of where the engine mounts.) Ride it around a bit to get a feel for how it rides. Go with ur gut. It it has some minor issues, nothing a little time and research and minimal money cant fix. Parts for these things are everywhere. Buying used, always try to get some money off. Offer $1000 and work ur way around from there.
Possible to get a picture of it? We can look at it and see if we notice anything weird.