It's pretty sleezy (or worse) for another "real" yacht broker to be circumventing the listing standard listing process that way. My general view is that if someone has a boni fide buyer, I'd just refer the contact to your broker. I'd have them track down the group pimping their business directly to you.

If they have boni fide buyer, then the other "broker" should be presenting them in accord with the general business practices. If they don't subscribe to those niceties, then they can make a net proposal to you: you take care of your broker and the buyer takes care of his.

My guess, they're just trolling.