Did they run the outboard when they took it out of the shed?
If they did and ran it on straight fuel for more then an extremely short time then the motor can be turned into either a reef or anchor.
If the marine dude thinks it only needs a bit of a service then get him to do it as long as there is a guarantee that that's all that's wrong with it.
Shove a bore scope or inspection camera down the bores and have a gander.
What area are you in?