Angela posts two sign-up sheets at the head of the dock. The first is for boats to sign up if they want to be extorted by goblins, and the second is for the goblins themselves (or rather their parents) to sign up. This way the kids know which boats to visit, and the boats know how many kids are coming. Isn't that great?
And then at the end of the extortion run, out at the end of G Dock, there is a party! (There are rumors that grog may be part of the run for the adult participants, but I can neither confirm nor deny that.)