The seller is just telling you that you've negotiated your best price and there is no more room.
If you want the boat go for the survey. Remember the survey, for all intense & purposes, is so you can get insurance and know the boat is safe.
They are not intended, as many people try to use them, as a further negotiation tool. Sounds to me like the seller is an experienced seller and been through the nickle & dime dance before.
I agree, the seller may tell you anything he wants. His personal experience is not something I am interested in and he probably feels the same way about me. It's just business.
As for rest, I respectfully disagree.
For example, insurance surveys don't test engine compression, they only care if it runs, isn't leaking fuel into the bilge, and isn't about to fall off it's mounts.
Some buyers are not inclined to look at the nuts and bolts. We all know people who are brilliant, yet can't seem to attach the socket to the end of the ratchet.
For many, when getting involved in a large purchase we let our emotions get in the way of the decision making process.
There are plenty of dishonest brokers and sellers. A good
surveyor is like having a good
lawyer on your side. He finds the mechanical and structural loop holes, the things the buyer may not understand, explains them to you and assists you in making an informed decision.