If you are putting down a deposit with your offer,

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If you want your offer to be taken seriously, or even be legally binding on the
seller, you must present some "consideration" for the seller to accept.
Otherwise, you can haul the boat (at your expense), have it surveyed (at your
expense), and if the seller gets a more attractive offer three hours before
closing he can simply junk you and your offer in favor of another. Your offer
isn't actually an offer without some consideration, and there is no compelling
reason for the seller to withdraw the vessel from active sale.

If you are using a broker, the deposit will be held in "escrow". If you're not
using a broker, see if a local marine finance company will agree to act as
escrow agent and prepare closing documents for a modest fee.