I have had similar experiences with brokers. The fellow we used to sell our boat and to help us buy our new (to us) boat was great. Very little (if any) BS, spent hours with us showing us boats, advising us as to suitability for us (after fully determining what we wanted), etc.
However, the other brokers (listing agents) were mostly a different matter. (To be fair, there was one or two that seemed pretty good). In one case, where the boat was moored at the Brokerage's marina (and he would not allow us to bring our own broker - first tell tale sign of a problem in my opinion), the boat had both a propane tank and a gas can stored in the cockpit lazerette which also contained a stern thruster motor, battery charger, and 2 - 12 volt batteries. Can you say BOOM!
After inspecting the boat, we found one of the stringers had at one point separated from the hull, and had been "repaired" using some type of caulk to "fill the gap". We contacted the boat builder (and they were fantastic and a big help) for advise and they informed us that this could be a very big problem (but difficult to tell for sure from only photos) and that the repair in any case was not adequate. This broker told us: " it's not a big problem at all and that stringers are not important"! On top of this, the seller didn't want to deal with the issue either in price or actually fixing the problem.
We walked, no actually we ran, and will never return to this broker. By the way, even though we couldn't involve our broker with the above boat, our broker still offered lots of advice and counselling. Above and beyond, in my opinion. He was involved in our final purchase.
Good advice from the others about asking questions where you already know the answer. It will give you an indication as to their honesty, knowledge, and maybe willingness to find out if they don't know.
Regards,
Tom