My attitude, both as a seller and as a buyer, is that the offer is the buyer's problem. If I had an offer but the buyer wasn't sure if they had the cash, then I would leave the boat on the market until the deal was concluded. It's not done until I have the cash in hand. I would add "Deal pending" to my listing, but I would not take it off the market.
Besides that, I think it's odd that someone would make an offer without knowing they can fulfill their end of the deal. I always knew what I could spend before making any offer ... On anything, boat, house, car.
Why go fast, when you can go slow.