Sorry to break in, but I would advise not to sell even if his "agent" shows up with cash. Don't try to outsmart him using whatever you think is a safe system to sell the boat. This person wants to rob you and your greed is his main weapon, so don't WANT to sell to him. Report to the authorities (there is indication of how somewhere in this thread) and refrain from doing ANY business with him. Avoid ANY contact.
Take care,
Luiz Schechter