Look at the stringers or runners in the bottom. These are usually 2x4" or 1x4" under the fiberglass. Make sure they are solid. Look at the bottom and make sure you can't see wood sticking through the fiberglass.
Look at the metal work. Does it look like someone knew what they were doing? Welds consistent, not lots of extra metal, muffler clamps and plumbers tape holding things together etc....
Does the steering work free? Gas pedal work and return to idle when you let off?
Engine start when the button is pushed? Make racket when it is being turned over?
Look at the prop for cracks or gouges in the metal leading edges. HOpefully it has 6 (six) bolts holding it on the crank and none are missing or loose
Do all the gauges work and the lights?
Radiator in good shape, no cracks, leaks not too many repaired spots?
Wiring look good or is it a rats nest?
Does the boat fit your needs? When you climb up and down from the seats, how does it feel to you?