I have bought three boats out of state and sold one. The first and last, I traveled to the location and inspected the boat myself. The middle one my brother did, and there was some undisclosed damaged. Before buying my current boat, I also drove(12 hrs) to a dealer to look at a boat, and it was blatantly misrepresented (1,400 hrs vs 1,000, scraps through gelcoat and a soft spot in floor…). It seems like you have done an excellent job talking with seller and others. I would recommend traveling to inspect the boat yourself or hiring an independent dealer to do an inspection or survey. I don’t know the price range your shopping, but a thorough inspection should only be a small portion of the purchase price. This would also help you in a dispute with the shipper if the boat was damaged in transit.
RE: #4 Make sure you insure the boat at the time of purchase.