A boat's price...
is what you, the buyer, is willing to pay. Having worked as broker, clean boats in really good condition (every thing works) that are priced "fairly" sell quickly. As others suggest below, once you get a sense of the price range for the boat you are interested in from the many sources available (and my sense is that comparables in your area are the most useful measure as NADA guides, etc., always seem to overprice boats), you negotiate a price with the seller contingent upon having the boat surveyed by a surveyor of your choice, which should include a sea trial. In this area (mid-Atlantic), most buyers begin the process by offering about 90 per cent of the asking price, if the original asking price was, in your opinion, fair to begin with. You also need to come to agreement with the seller about what the results of the survey may mean in regard to the final price. Some sellers will negotiate a price reduction for items found during survey, others will not. Find out before the survey. Good luck.