In the case of the real estate example, I bought my last house with a broker in 2005 that saw our finances and decided we needed a bigger house x2. We hesitated, but we were eventually convinced by our broker in spite of our original instructions. Because of that, this housing crisis hit us harder and impacted our cruising plans to a far greater extent than if we had stuck to our guns and fought our broker.
Fowler, not to be too harsh, but it almost sounds as if you would walk into a Chevy dealership looking for a used Town and Country, walk out with a new Corvette and blame the salesperson.
You don't need a buyers broker. Go to Yachtworld.com and start doing searches for boats that do meet your criterion. If you find a boat you like, then contact that broker and look at the boat. The advantage to you is that you would have no relationship with these brokers so it may be easier for you to tell them "no". Ultimately, it is you that has to make the decision.
If you really don't want to deal with brokers at all, then just search for private sales. In this economy I would think there would be plenty. You also could use the technique of wandering the marinas and identifying boats that look abandoned then contacting their owners to make an offer. There are may be boat owners out there that would like to unload their boats but never bother because they don't trust brokers and don't know how to go about it themselves.
If you have any good friends who are knowledgeable about boats, then it may be a good idea to take them along with you to help. If you don't know anyone, then you might try and find a marine surveyor who you might be able to negotiate a deal where they can accompany you to look at the boats. These won't be surveys, and it would cost you a fair bit, but you could get some more objective advice that way.