We're seeing a lot of game playing in listing of houses and boats. Some may intend to sell, although they don't expect to get the asking price. Others are just tossing out numbers they wouldn't refuse to sell. Asking prices and prices one will accept have no consistent relationship. I've seen houses bought and 50% more asked, but then sold for only 10% more. I think if they did buy the boat expecting to flip it, then they may have just made a huge mistake. It's not worth what they're asking and in a couple of months, if things go as I expect, they'll likely not be able to even net what they paid.
People see a market moving up and think there's no limit and things will continue. Your attitude, RTF, is reasonable. You are comfortable with what you got. If they buyer makes a nice profit, great, but not likely to happen.
I remember long, long ago, my mother sold her house the week it was listed. Oh, she worried she'd sold it too cheap. Buyers lived in it six months, relocated and put it on the market for $33k more. She wasn't happy to see that. Then they dropped the price many times over the next 2 years. Over 2 years after buying it, they sold it and after paying realtors they lost $5k. It had become a stale listing and no one looking, figuring something must be wrong. Only thing wrong was the pricing.
We're already seeing the prices dropping on listed houses and I'm sure it's happening on boats. The window for buying and flipping a boat, without making major improvements to it, is very short and I think your buyer already missed it. Will be interesting to follow.