Also, ask who the boat owner used for repairs and make a point to talk to them. It's a good idea to have a qualified marine mechanic thoroughly inspect the boat before purchasing it. If you are going to do it yourself check the spark arrestors and plugs, alternator, belts, hoses, strainer, blower, shift cables, engine alignment, etc. Analyze the oil and make sure it is not cloudy or gritty Cloudy oil can mean the engine block is cracked. Feel free to tap on the hull all the way around and make sure the hull is consistently solid.
Mismatched paint is a sign the boat has been in an accident.
Also check for gelcoat blisters and dry rot. Any of these things can throw off the performance of the boat. Check for ripped seams and color fading. Also check the boat cover if there is one. It's nice if the owner will sell the boat with a few extras which are probably already on the boat.