IF someone wants to sea trial your boat, both in and out of the water survey, THEY will pay for it, not you. That includes taking it out of the water, blocking it and rewrapping it. End of story. Tell him, make no concessions. Dont split the costs, why? Because you are content the way your boat is now, out of the water, blocked and wrapped.
Unless he is going to pay for everything just tell him, "See me in the summer."
If he wants you to remove the boat from more offers then, a non-refundable deposit which, if he is satisfied with the sea trial, you will gladly take the amount off the price. If he is not happy with the boat after sea trials, YOU keep the deposit because you have removed it from the market.
Understand, the deposit is non-refundable because you are not accepting other offers.
Now, go back and count the times I said, "non-refundable deposit and, you have removed it from the market and other offers."
In my mind, that is the end of the story.
I agree with you Dan - and that is exactly what we have done in the past.