What the going rate is and the actual rate is when a deal is on the table are 2 different things. I've sold boats where I've compromised and the broker has compromised just to get the deal and the broker has ended up with less than 5% + VAT but 5% on something is a lot better than 8% on nothing. Obviously a broker is not going to agree this kind of thing up front
I think it can depend if the broker thinks you are asking a realistic price. If you are prepared to price to sell then you can ask the broker to help you make a quick sale which is cash for you both.
Also remember that there are different brokers some small with only a local database and some with national and even international reach. The added exposure might be worth extra money to you depending on how serious you are about selling
I'd love to keep it but we live an impractical distance from the sea (3-4 hours drive in any direction!). Plus I'd like to upgrade my river boat with some of the proceeds. I think it's better all round if it passes brand new to the next owner who hopefully can use it more often than we could.