Try being totally honest with the broker you contact. Let them know what your budget is, if you have to get financed or can pay cash, what type of boat you are looking for, and how quickly your ready to buy if he finds a boat the meets your requirements. Many folks spend years dreaming about buying a boat, and make a hobby of looking at them. There is nothing wrong with that, but don't expect a broker to invest hours of his time working with you if you appear to be just a hull kicker. Sometimes they can be wrong and miss a sale, but it's up to you to convince them your serious.
Ton's of hobbyist boat shoppers, then lots who are serious but have no idea about what and take decades.
Your advice to be honest and share information is excellent. Let them know you and you know them. Then if not a match move to the next one.
Think of those who pop in here and ask a question while providing no information on which we can base an answer, questions like "what trawler do you recommend?" and they don't even tell you where they are, what their experience is, how they intend to use it. Then you ask and they're still not forthcoming.
Boat brokers know those who are just running through the YachtWorld listings. The good ones offer their services in assisting on the search, but most won't put much effort in if it's just to answer questions on one boat. Yet, I've known brokers who went way out of their way for someone who shared everything about their interest and knowledge but stated up front it would be two or three years before they bought, explaining why. A broker I know then asks if it's ok for him to follow up with him periodically, that even though he knows he's not ready to buy, he might email him information on specific boats knowing that might help them when the time comes. He sends one email a month oh what he calls his followup day he sets aside for that. Once buyer took five years but bought from him. Another who said he wouldn't buy for two or three years loved the first boat he was sent and still said, "I know I can't buy yet but would it be possible to look at it?" Well, plans changed as it was love at first sight.
The brokers I like most don't push, but lead. They don't sell boats but they sell a service of assisting you in finding the best boat for your needs.
They also accept what you say at face value. Now, I get annoyed at a sales person who won't do that and won't listen. I don't like game playing on either side.