I don't see any scumbags in this deal on either side. I just wish you guys could handle the problem between yourselves.
I have bought several boats without sea trials including my current Tiger. I did have a good survey done including mechanical and knew the history of the boat. This one turned out better than expected.
Other times. I haven't been as lucky.
If you want a survey, insist on picking your own surveyor. If you sea trial and somesthing doesn't seem right, walk away.
On a used boat, it's usually your problem from about the time you hook it to the back of your truck.
On a personal level, I feel bad for both parties that a problem popped up. No one wants that. Not buyer or seller.