Transom/ stringer rot

[SkunkBoat]

what they said plus...

the boat picture has been painted. That usually implies that some repair work has already been done which is usually a good thing (why would you paint something without fixing it first?). BUT you never know...

Inspect fuel tank, preferably by removing the hatch, not just the round ports.
It will be foamed in. Look for corroded aluminum tank, stripped screws in sending unit, old hoses, wet foam...you also get a peek at the stringers in there.

if allowed, remove a screw low on the transom, like a transducer screw. Does water come out?

Put your weight on the lower unit and see if the transom flexes.

nowdays you can get a flexible camera pretty cheap, use one in every hole you can find.