do a water test if you can. Check for cavitation when you launch it from idle. Check to make sure the engine runs smoothly. Check for black spots on the J-pipe indicating a leaking exhaust. Check for oil in the hull or on the engine (run your finger under things in case they pressure washed it). Make sure the cables all work smoothly (throttle and steering). Any maintenance records would be good to have. You can actually crawl up and look at the prop with a flash light. You should be able to see the leading edges and teh general shape of the wear ring from there.