It is my belief that, while it shows negatively on his character, a con man should still receive punishment, whether he was conned himself or not. If the con man is gaining money from a con, it is illegal. He has already done something worth being punished for, as has the second con man. It does not matter if the con man was conned - what he did was against the law.
People who con other people out of money are the most clever and the worst human beings you would ever meet. They work hard to screw people out of money and they do not care. It does not matter if they have been conned themselves, they need to be punished for their crimes.
Just because someone is conned does not give them the right to con others. If someone chooses to believe a con and then goes on to further con others, they deserve exactly the same punishment as the original person doing the con. Bad behavior in others does not excuse bad behavior in ones self.
Con men should be held accountable and punished for any crimes committed. However, if a con man is conned himself, there is no need for additional punishment; just the punishment he has coming to him. Con games are serious crimes, and should be severely prosecuted. In short, if a con man gets conned himself, he has it coming to him.