In this "phone-tag" world I think I'd be reluctant to get too many "middlemen" involved. In our latest sale/purchase we were lucky to sell privately and then buy through the listing broker in what was really quite a positive experience. In the process of searching out the next boat, we always approached the listing brokers (more direct and quicker access to information). We certainly ran into some "used car salesmen" along the way but also dealt with sincere, knowledgable individuals as well. It's really the luck of the draw as to the boat which interests you being listed with a decent broker.
Actually engaging a broker to search for you is not common practice in our area, but we have let local brokers know what we are looking for, and did get some callbacks a time or two when a new listing arrived. I don't think there is a lot of MLS type of cooperation between brokers as a rule.