i have only boat 1 boat through a broker. Mark at Stingray at cobbs. As a buyer, i found him straightforward and easy to deal with. There are always the issues of what they try to get away with (in my case it was a dud trailer), but that is part of buying boats.
As a seller, I have spoken to him several times after and phones me when people are interested in my kind of boat. he charges a flat 6%.
I have used Blue lagoon for servicing and repairs, but he does seem to do a lot of repossessions for sale. Have seen him a rockely taking boats on repo.