I would take a real close look at the transom....it could be dry rot on the inside and not really visable on the outside. If you have a marina available have them check it out. They should have a moisture meter that would tell you the moisture content of the transom...lower the better...If no marina is available take a sharp pointed object ( ice pick, awl, ect.), find a spot near center and above the water line and poke it into the transom...if it pokes hard all the way in..should be ok...if hard at first (fibergalss) then soft (easy to push) that would mean soft wood and I would not buy the boat.....
If the owner has offerd to take you out, the it might be that the tansom is good (safe) or it might be he does not even know he has a bad transom....
I might be a little "gun shy" when it comes to transoms because...I am speaking from experiance....buying a fiberglass boat what appeared to be awesome turned out to have a bad transom....not even safe to operate...been there done that....
Outdoorsman.