I feel your pain, amigo
I know how you feel all too well. There's a lot of good advice above.
As far as using your own broker, it's pretty much dependent on how much work you want to delegate and how much you want to do yourself. As the Fool has wisely stated, a broker can weed and cull through a whole lot of boats that are NO WHERE NEAR as good as they look in a listing. I've found recently that a bunch of the photos used are -- ahem -- not quite recent or representatve of the actual condition of the boats in question.
As far as trying to zero in on an offer price, that's a bit of a challenge. It's true that "your" broker can pull a "sold boat" report off of BoatWizard -- which is a firewalled part of the YachtWorld database. However, don't forget that surveyors also use this same service. If you can, spend some time on the phone with a trusted surveyor or two and see if they can't steer you in the right direction.
Keep in mind that some owners may not be willing to part with their baby for a price as paltry as fair market value -- don't take it personally, just keep looking!
Best of luck,