I had contacted the broker's office from an ad I had seen. The broker met us, took us down to the boat and gave us a tour... but was pretty non-committal about everything. (trying to stay as neutral as possible, no doubt)
After we had inspected the boat to our satisfaction (and took loads and loads of photos), the broker took us back to the office and outlined the process...
We wanted a sea trial, a survey and a haul out. The broker arranged all that (used the surveyor I asked for) and went with us on each of these events, the broker also made arrangements with the marina for us, as we needed some time before we could actually pick up the boat.
Ultimately we made an offer and the broker acted as the middle man between the seller and ourselves... delivering offers and counter offers until we settled on a price all were agreed to.
To us it was a lot like buying a house... with the broker ensuring that all the papers were in order, and all parties were satisfied, and all the arrangements that had to be made were made. We paid cash, so there was no loan arrangement.
Subsequently, I have discovered that some of the systems were not quite as advertised, but in the end, these were minor quibbling points that might have changed the offer by a boat buck or so.