Stories like "Dusk" and "The Umbrella Man" owe their existence to the great American genius Edgar Allan Poe, who published an essay titled "Diddling" in 1850. "Diddling" was the term Poe used to discuss what is now called "conning," "scamming," and many other things. Poe states:
Diddling, rightly considered, is a compound, of which the ingredients are minuteness, interest, perseverance, ingenuity, audacity, nonchalance, originality, impertinence, and grin.
He does on to define each of those terms that make up the personality and craft of the diddler and then devotes the remainder of his essay to examples of diddling. It is interesting to see what kinds of confidence tricks were played in Poe's time, which was before the Civil War. One of them is selling furniture the seller does not own. Another is finding a "lost" wallet full of currency which turns out to be counterfeit.
A bold diddle is this. A camp-meeting, or something similar, is to be held at a certain spot which is accessible only by means of a free bridge. A diddler stations himself upon this bridge, respectfully informs all passers by of the new county law, which establishes a toll of one cent for foot passengers, two for horses and donkeys, and so forth, and so forth.
There are several noteworthy similarities between the diddlers in "Dusk" and "The Umbrella Man." For one thing, they are not pretending to be needy but just the opposite. The young man who tells Gortsby the story of the lost hotel pretends to have plenty of money but only needs to borrow enough to rent a room for the night. The elderly gentleman pretends he can afford to take a taxi home every day after his long walk, and he carries a silk umbrella worth twenty pounds which he offers to sell for only a pound.
In both "Dusk" and "The Umbrella Man" the diddler is not really asking the person he intends to diddle to give him money. The young man in "Dusk" pretends that he only needs a loan which he fully intends to repay by mail within a day or two. The umbrella man is offering the narrator's mother a silk umbrella worth twenty pounds for only one pound. The mother is a victim only in so far as she knows she is a receiver of stolen property and a co-conspirator with the diddler. The author of "The Umbrella Man" does not say what she will do with the "hot" umbrella, but she would have no way of returning it to its rightful owner.
Both the young diddler in "Dusk" and the elderly gentleman in "The Umbrella Man" share most if not all of the characteristics Poe calls the ingredients of diddling. Both show "perseverance," "audacity," "nonchalance," "originality," and "impertinence." What Poe means by "grin" is a grin of satisfaction at having succeeded.
Your true diddler winds up all with a grin. . . . a diddle would be no diddle without a grin.
We do not see the diddlers grinning in "Dusk" or "The Umbrella Man," but we can certainly imagine the young man grinning and even laughing when he is safely away from Gortsby and has acquired a sovereign and a cake of expensive soap. And we can imagine the umbrella man grinning at himself in the mirror every time he downs a triple-shot of good Scotch whiskey and sets the empty glass down on the bar.
So it appears that Poe has the topic of diddling pretty well covered and that the diddlers in "Dusk" and "The Umbrella Man" are similar in all the ways Poe specifies: minuteness, interest, perseverance, ingenuity, audacity, nonchalance, originality, impertinence, and grin.