It creates a legal contract. Without some consideration given and received, you do not have a contract. That means that the seller could "accept" your offer, but still sell the boat to someone else.
Oops! You already paid for a haul-out and survey? Too bad. That was a contract between you and the surveyor, not between you and the seller. Without a deposit you could arrive on the day of the closing only to hear the seller say, "Tough luck, but I sold it to someone else yesterday."
With the deposit, there is now a legal contract between you and the seller, and if he breaks that contract then you have recourse.
Denver,
True, but consideration doesn't have to be a "deposit" and can be $10 OVC, which I usually use.
As far as a "legal" contract the cost of enforcing it is often not worth it if either the seller or buyer backs out. The seller could have sold it to someone else right after your survey and sea trial, and not much you can really to that's practical. Now, one can protect themselves somewhat with a non refundable deposit (from either party, depending) to guarantee performance. I've done that on occasion, from both the buyer and seller side.
My point, is the typical fully refundable deposit doesn't do much. Maybe it makes the seller "feel good", but if refundable, what's the point. I'd never put down any deposit unless it would smooth out the deal and only then with MY representative. I've also rarely had a problem with any broker regarding this, and have never put a deposit into their account, yet.
As a buyer, my first goal is to get enough info to see if this is really a good deal. That will require getting a lot of info from the seller, and expecting him to provide good info, which can be verified later. This process may or may not take a bit of time.... and the more time, the more likely of success. If the boat is local, I may visit it a few times, perhaps bring a boating friend with (that has skills). I'll also ask for a short sea trial, and I'm willing to pay the expenses for, fuel, captain, etc. That way the seller is covered for his expenses should I not buy. However, most of the sellers I've done this with refuse any money and we very gracious with the sea trial.
Occasionally there's a killer deal, and have to act fast. In those cases I have no problem buying without a survey, but the numbers have to be really good. I do try to still do a sea trial and mechanical check.
I've never been burned with a boat purchase. Some ended up better than others, but all good. And in all the surveys inspections, sea trials I've done, there's ALWAYS something that's missed or unknown at the time of purchase that shows up later. "Oh, we should have thought of ......"
Now, as a seller.....
I doll the boat up, be sure it's REALLY clean and everything is working.... Try to make it sell itself. If ANYONE shows up, I'll take them for a ride to "sell" them the boat, which has worked will over the years. I've never had a joy rider show up. Sure, there are a few low ball offers and folks that just aren't interested enough to buy, but occasionally I've convinced them to come up to my price. The effort in "selling" the boat is small compared to the benefit of getting it sold.