Seller doesn't have to do or pay anything if he doesn't want to. The boat may be listed for sale "as is - where is" in which case the selling price may be so low, the seller will not bear anymore expenses.
As I said, the buyer offers a contract with price and all terms and conditions and the seller can either accept, decline or counter-offer.
Of course, in today's boating market, boat sellers will have to do anything and everything in order to sell a boat.