I used to be a broker so can give you my opinion from the inside.
Yes the broker will be getting a commission, but I also found that much of the time, boats that were for sale
by owner only were priced higher than the same model I was selling. I would attribute that to owners that were too emotionally attached to the boat or that had an inflated idea of the value. So, buying from a broker does not necessarily mean you pay more.
A "good" broker (I'll be the first to admit that there are a lot of bums in the business) will help you select the right boat, steer you away from the lemons and guide you through the paperwork process including clear title, documentation
If you are buying a boat a long way from where you live the broker can also set up appointments so you have boats waiting to see when you hit town. Again a good broker will also know if the listed boats are in good condition or sinking at the dock
I think more important will be a good surveyor
. If you end up buying a boat in FL let me know, I have a really good one to recommend.