Look it over like anything for excessive wear. Make sure trailer looks good, bearing not hot if it was towed, not bent like it was wrecked or jack knifed. Boat, not huge marks from hitting something, shoddy patch jobs in toons, no soft spots in floor, carpet and upolstry condition should be obvious. Look under the dash, hope there is not some rat nest where some one went to hacking and spicking wires that will be trouble for you. All the switches and running lights work, live well if it has one. The motor will be like any outboard. Look it over pull the hood assess outside condition. If you really want to get into it pull a plug or two and peek at the cylinder walls. Make sure it engages and does not jump in and out of gear. That it goes wide open and that it can come back down and idle, that it can idle and not shut off, does not stumble. Gears do not grind or pop while your doing anything other than maybe small amount at a shift but none is what you wnat. Oh and DO NOT buy it without test driving it. I don't care if this means yall have to drive a half hour to the water. Any of the motor things are not a deal breaker depending on your skill or ability just barging power.
