Well it's a 2001 so it probly couldn't have seen enough abuse to be permenently damaged/worn. Sometimes obvious things like they say "Ohh its never been raced" and yet theres numbers on it, or ask how old the chain and sprokets are, if they say they're new or only a few rides, look closely at the teeth on either of them, and check how worn chain is (tug on it at the back of the rear sproket, if it pulls away more than half a tooth then it sure aint new. Just like with cars most people just alwase answer your questions positivly so if you know they're lying about some then they may be on the others. Some other tests or stuff to look for,
-When test riding it, start it up and put it in gear, with the clutch pulled when you rev the engine if the bike creeps forward a littlebit that can tell you it needs clutch work.
-ride in 3'rd gear and start applying the rear brake while accelerating, pay attention if the clutch is slipping, and if it pops out of gear, then theres transmittion trouble.
I guess you could spend a whold day test riding, interrogating the owner, and inspecting, but if you see no physical damage, and even if the clutch is worn or top end needs replacement that stuff doesnt cost to much, and will help you connect with your new machine. That is if your getting a good deal, how much is it by the way? Like Racer#213 said, ask simple questions and see how quick the andsers come, also see if he points out any faults or trys to avoid them. Hope this helps
-Jim