I always go to the store and buy a local sled trader and see what they are going for in my area. As far as what to look for.......listen for any weird engine noises.Go for a ride if you can. If not put the back up on a stand and run the machine. Listen for any clunks in the drivetrain. Check the suspension to make sure the shock aren't spungy and it doesn't bottom out or else you will end up rebuiding them. Check the condition of the track....how much lug is left? if it was studded if there are any ripped out studs? Also if it was studded look up at the heat exchangers(coolers) in the tunnel and see if there are any scrape marks. Always pull the dipstick on the chaincase and check the oil level and see if there is an excessive amount of metal on the magnet.If you have access to a compression tester I would definately check both cylinders....compression is to low then you need rings or possibly a top end rebuild. Good luck!