Unused boats break down more often because of dry rot of rubber, dead batteries, water in the gas and a host of other problems. But aside from that check the transom, get a compression check on the motor, is the prop bent out of whack? What does the bottom of the hull look like any holes or chipped glass? Take it for a test ride, is it hard to start? Walk around the deck to see if there are any soft spots that would indicate a problem. Condition of the tires and bearings on the trailer. Is there a spare? I would check everything possible and just take note of what is wrong or missing and just budget for the replacement or addition of the items. If your budget allows do not get an underpowered boat, you will regret it later.
Good Luck, Don