My 2 cents:
I've never had to use a broker. I've bought and sold a number of boats. I've seen lots for sale without a trailer. You've got by for years, I'll guess, without a trailer so others can to. It does limit the potential buyers but if you are near a popular boating place with full service marinas many times no trailer is needed. The buyer might be able to borrow a trailer to haul it to a marina or pay someone to haul it for them.
Getting the word out is the biggest issue. I've used facebook market place and facebook boating groups to buy and sell boats. I sold my 50 ft Houseboat by listing it on ebay. It did not sell there but a potential buyer set up an appointment and ended up buying. Craigslist is another free place to list your boat. A person shopping for a boat will look all over trying to find the right boat at the right price. Boat Trader is a good resource but you have to pay to advertise there.
You might also look around to see if you see any trailers for sale that fit your boat. Not that you would buy it, but you could let potential buyers know there is a trailer available.
Good luck.