Symbolism, Imagery, Allegory
Con artists want money, but that's not the only reason coin gets play in this text. In fact, what's more interesting is how the question of confidence so closely precedes a request for money: Do you trust me? Can I has your monies? The two go hand-in-hand in this text, and money—as currency—seems to be the means of proving your trust.
Plus, there's totes a connection with the barber's "No Trust" sign indicating he doesn't accept credit. No fiscal trust here equates to no social trust, and Frank is miffed at the barber over this.
Why does money get this kind of overlap with confidence? Well, for one thing, money and a country's currency—even when still tied to a gold standard—requires a certain faith in that nation's economy. The economy is a function of society, and many of the ways humans interact with one another is through some sort of financial exchange.
What happens when you further strain the relationship between confidence in others and your money? You get this scene about a lack of faith in money itself:
"What a peck of trouble that Detector makes for you now; believe me, the bill is good; don't be so distrustful. Proves what I've always thought, that much of the want of confidence, in these days, is owing to these Counterfeit Detectors you see on every desk and counter. Puts people up to suspecting good bills. Throw it away, I beg, if only because of the trouble it breeds you."
"No; it's troublesome, but I think I'll keep it.—Stay, now, here's another sign. It says that, if the bill is good, it must have in one corner, mixed in with the vignette, the figure of a goose, very small, indeed, all but microscopic; and, for added precaution, like the figure of Napoleon outlined by the tree, not observable, even if magnified, unless the attention is directed to it. Now, pore over it as I will, I can't see this goose."
"Can't see the goose? why, I can; and a famous goose it is. There" (reaching over and pointing to a spot in the vignette).
"I don't see it—dear me—I don't see the goose. Is it a real goose?"
"A perfect goose; beautiful goose." (45, 105-109)
This conversation between Frank and the old man at the end of the book is hilarious and depressing. The old man has just gotten a freebie from a sales-boy that's turning out to be more trouble than it's worth: a counterfeit detector that's making the old man doubt all of his bills are true. He's poring over his money trying to find various images that the directions say are unobservable even if magnified. That's some mischievous wild goose chase right there.
If you can't even trust your money is real, what—and who—can you put your faith in? What good is your word? Maybe this is why, "put your money where your mouth is," gets trotted out for bets whenever someone talks a big game. The challenge: tie your word to something you may care about more (cold hard cash). Just be sure your cash is legit.
Money and good faith problems get even trickier when you think about Winsome and Egbert's stance about not diluting the "purity" of friendship with the contractual obligations of money. For these two, money and friendship cannot coexist.
When money is introduced, the interaction is either a strict contract or a donation (though they'd definitely reject anyone asking for one of those). What do you think, though? Do the bonds of friendship demand a vote of confidence if someone is in need? What's the best way to handle a loan (gift?) to a buddy?