Deposits and Offers
It's a common misconception that the deposit is consideration. Legally, the deposit is merely another term of the contract. The consideration is technically the promise inherently included in the contract to fulfill all the agreed terms of the agreement.
A deposit can certainly be submitted with an offer, but should not be cashed until a contract is made since the deposit is, as I said, just another term of the yet to be agreed contract. So, aside from a broker's personal incentive, which is of no serious concern to the parties of the negotiations, there's really no justifiable motivation for a party to the proposed contract to demand or submit a deposit with the offer.
However, once a contract has been made, the deposit should, by agreement, be submitted and processed by a certain agreed date and held either in trust by the brokerage, or in the case of a private sale, in a non-interest-bearing segregated or non-segregated account pending the outcome of the conditional contract. Who holds the deposit and the terms under which is is to be returned or forfeited are, of course, subject to negotiation of the parties.
The problem with the marine sales industry is that there seems to be no oversight by a governmental body or responsible national organization. And there's certainly no ethical standards, or even contract standards. My own experience with the industry left me feeling that I had been maliciously deceived for personal gain by the brokerage who was supposedly representing my interests.
My trawler is for sale
https://www.boatdealers.ca/boats-for-sale/383503/monk-mc-cruiser-42-georgian-bay-ontario privately, and I've amended what I was told was a standard contract. I found it highly deficient. It failed in clarity and completeness. The revised version is far better at protecting both parties, thus leaving little room for misunderstanding of terms. And it also reduces the possibility of litigation for a failed contract, unless, of course, one of the party reneges on his or her agreement.
I hope this helps clarify this matter. Bottom line? How and when and the amount of the deposit is subject to negotiation by the parties of the proposed contract, and not by the brokerages involved.