Any advice on purchasing a used sled would be appreciated from making sure it is not stolen + leins. To actually checking the sled over to make sure it is in good mechanical condition.
Cheers,
With regards to the mechanical aspects of a machine look for straightness throughout the tunnel, motor area (supports in and around the motor) and the front end, compression test, crank runout, clutch work that has been done. How clean is the sled indicating how well it was looked after.
Other fine peeps will chime in and give you a few more pointers as more and more peeps see your request.