Personally, I tend not to use a surveyor recommended by the broker in the first place unless you are very comfortable with the broker. Nevermind having the broker, who stands to collect anywhere from 2-10% of the purchase price of your boat if and when you close, do the survey.
Not that I am insanely paranoid, but unless you have a signed buyer-broker arrangement with this guy or you are married into his family I would find an independent surveyor who has your interest in mind.
You are about to make a sizable purchase, and even a survey isn''t cheap. You need someone absolutley, irrefutably 100% in your court.
Like any business there are honest & dishonest people. So - trust your broker for doing the deal with him in the first place, but cut the cards by using your own surveyor.