What even is a confidence-man? Glad you asked.
Whether playing the short or long con, a confidence-man is someone who tricks you into doing something. More often than not, that something is parting with your cold hard cash. Although the title focuses on a singular figure (the con artist), you can't have a con artist without people lining up to be conned, so there's also a certain kind of relationship that's implied here.
But hold up. Just exactly who is the confidence-man in the title? The truth is that we never can quite tell. People manipulate each other left and right in this novel, and we never quite know who has the upper hand or who is up to what. We're just as much in the dark as the characters on the Fidèle are. Maybe the confidence-man of the title is the devil, morphing into various characters. Or maybe not. All we know is that conning is happening. Or is it?
All the suspected con-men in this novel are bent on "correcting" the lack of confidence people have in one another. "Wouldn't the world be a better place if we all believed in each other?" they ask. It's hard to tell if this is decent advice or another trick.
Con artists operate by getting you to doubt yourself, your instincts, and your senses. In that respect, Melville himself is a supreme con artist, and we as readers are just sitting ducks, along for the ride.