I have very mixed feelings about boat brokers. They tend to be a prickly bunch. I say this even though I have many friends who are brokers and are wonderful people. If you have a difficult boat to sell they can be helpful. Many brokers have very visible dock space in highly trafficked marinas, so if have a boat that benefits from that kind of exposure, they can be a good value. And, you can't get into Yacht World on your own (even as a broker you have to have 3 boats listed).
But 10% is outrageous. Just like 6% is outrageous for a house. I have had good and bad experiences with brokers, but even with the best of them >$100k for selling a boat, even with marketing and moorage costs, just doesn't make sense.
Are there Redfin-like services out there for boats? As a serial entrepreneur with a boat broker's license, I was thinking about building a service that would help owners sell their own boats. Software that helps you price and list your boat, access to certified services for photography, surveys, escrow, titles, insurance, etc. Is there anything out there? In FL perhaps?
FWIW, I bought Gallivant without a broker (and got yelled at by one of the local brokers for stealing his commission). While I didn't have a broker, I did have a third party that helped the out-of-state seller work through the process. I arranged for all of the services including the survey, haul-out, and title work. The total for all of those fees was less than 1% and it went much more smoothly than the previous transaction that had brokers on both sides.
Would I pay a buyer's agent if I were listing my own boat? I think it depends on the listing price for the boat and how hot the market is for your boat. For higher $ value, I would offer the buyer's broker a fixed price, dependant on the sale price. If, like now, the market is really hot, most brokers around here are hurting for inventory. That gives you some leverage for pushing the commission down even lower.
Good luck!