I'll give you my .02 cents on the stolen issue. If they don't have a title for it, don't buy it. I'm not sure how it works out there but over here, we normally have titles that go with the bikes. Look at the identification numbers on the neck of the bike, usually right side, and make sure they aren't tampered with (ground, scratched off, restamped). Also look at the engine number for the same indications. If the seller balks at the idea of you checking the identification numbers through your local law enforcement agency then walk away. If it's too good of a deal to be true, then it probably is.
General info about what to look for on the bike itself in regards to mechanical issues, well, just look at it overall. Look for major dents, dings, scratches or major damage on the frame and plastics. Also look at the rims and chain/sprokets. See if they are worn out or bent. Look for oil leaks too all around the motor and finally ride it. See if it rides straight, bars not bent, frame not bent, shifting, stuff like that. There's alot to it so if someone could come with you that knows about bikes, that would be helpful. Good luck
Elk