Check the "deck" really well to see if there is any rust though that may need repair. My 60" Mott is balanced to the point that I can tip it back on its roller very easily by pulling the top of the A frame. That way you can see the condition of the blades and how many are missing plus the underside of the "deck". It would be nice to hear it "run up" if there is a tractor available. Of course check to see if the seals appear to leak. Check to see if there is any oil in the gearbox. Vibration is a killer on these units so it is important that one does not lose too many blades. Look at the grease fittings to see if there any evidence of maintence. Pull cover off and look at belt. Others here will chime in and fill in what I have left out.