I've put over 12K on my bike since october of last year and I have no doubt that it will see pretty high miles if its not taken out before then. If the maintenance is done and the person takes care of it a bike can see miles comparable to some cars. The problem is bikes rev much higher so they wear out faster if used that way. Many bikes don't get run very hard even though they can be. The only real gauge is knowing how it was maintained and ridden. Past that its a crap shoot, as people have said, you can kill a brand new one before its first oil change or you can have one from the 90's pushing 40K and still running strong.