I'm not going to post my guy, as I've been hearing some real mixed feedback about him lately. It's now been years, since I actually used him, but the trades in the area all seem to have a problem. Not sure it's legit or not, because I find most of the trades in the area to be awful too, but enough that I'm not going to take the chance.
As for advice, understand these guys almost exclusively work for the seller. They can be very helpful, some are more honest than others.
One strategy I've always liked is this. If you have a brand that you like and it's still made, see if the nearest dealer has a used broker on their staff. Sure, they'll first want to see what they have, but they often know every boat available and more about them than you would ever know. If you have a couple of brands, it's okay to make it clear that you are working with them on only brand X.
However, do not use multiple brokers without disclosure. They can and often do put a significant amount of time into finding you a boat. If you then buy through another, or they sense their odds are low with you, your calls will not be returned. You become a waste of their time. They do need to make a living and return calls to better prospects first.