broker sales contracts
If you are a buyer, remember that both brokers, the listing broker and "your" broker are getting paid by the seller. They are both technically "sellers' agents". They get paid by getting you to buy the boat. There are many honest brokers, they are just people, after all.
Many brokers use standard purchase/sale form contracts that are generally seller favorable. One of the really big things I've noticed is that the purchase and sale agreement says that the seller is making no warranties or representations. You have the right to, for instance, require the seller to state in writing that he is not aware of any material deficiencies in the boat, that he is not hiding or failing to disclose something important. This is an important concession to get from the seller, even if you have the boat surveyed. If might be hard to prove the seller knew something he didn't tell you, but you are a lot better off putting the seller on the spot before signing on the dotted line and making sure the contract language states that the sellers' warranty survives closing.
You have the right to add addendums and clauses for things that are important to you as a buyer, to move the deal away from a "caveat emptor" type of deal.