Before handing over your hard-earned, if it's not too late, you'd do well to tap all over the transom and floor with a solid object eg screwdriver handle, small hammer and listen. If it's in good shape, you'll get a hollow knock. If there's rot, you'll get more of a dull thud. Knock good, thud bad.
Know how to use a multimeter? If so, take one with you. The boat will almost certainly have ski hooks on the transom. Set the multimeter to measure resistance at a low level, then put the one probe on a ski hook and the other on an engine bolt. "0" (full resistance) is good. Any other number is bad. It means there's water in the transom which either already is, or will become, a problem. Do this both sides of the engine.
Good luck. If the boat, motor and trailer check out, you'll get a lot of pleasure out of it.