From my training back from my days working a real job: Actually, $10 bills are the most commonly counterfeited because nobody suspects them and they’re of enough value to rack up the profits pretty quickly (which is why $5’s and $1’s are almost never counterfeited). $20’s are the most frequently caught in retail transactions, normally because that’s the level that many retail stores require the use of the “special markers” or at least visual scanning.
That said, if someone paid with entirely counterfeit money, chances are they knew it from the get-go and any personal information supplied to you is bogus. [IANAL]You’d certainly wait to bring a complaint against them in small claims court if they refuse to compensate you, but chances are you’ll win a default judgement against a mystery person. If you know or are at least still in touch with the person, go to his bank with him and have him withdraw the cash in front of you and then hand it over. Otherwise, get your boat back.[/IANAL]
Before you even attempt to do that, however, you’ll want to contact the Secret Service, who is in charge of investigating counterfeit money (the bank may have already done so, but likely didn’t provide any identifying information regarding the suspect) and file a report through them. If you still have good contact info with the person you tried to sell the boat to, provide that. Even if the person unwittingly passed along the bills, they’ll want to know where he got them from so they can eventually track it to the source.