You'll want to drive it. Ask to see maintenance records. Check number of hours on motor (a used motor is better than one that has sat around with little use). If the seller won't let you test drive it, leave. Check the floor for soft spots. Check the transom- Bounce your weight up and down on the motor to make sure the transom is sound. Check the compression in all cylinders...they should be close to even. If you like what you drive, I'd ask the seller if you could take the boat to a mechanic for a buyer's evaluation...these are well worth the money assuming you are not a mechanic yourself.