In Saki's short story "Dusk," the narrator details the fact that "Dusk, to his mind, was the hour of the defeated." By stating this, one can assume that those who come out at dusk are those who are willing to, or need to, do anything not to feel that way.
The people who come out at dusk are those "who hid their fallen fortunes and dead hopes as far as possible from the scrutiny of the curious, came forth in this hour of gloaming, when their shabby clothes and bowed shoulders and unhappy eyes might pass unnoticed, or, at any rate, unrecognised." It seems that Saki is forcing the reader to be prejudice against those who appear at this late hour. They are hiding and need not be trusted. (Which adds some irony to the story based upon the fact that Norman Gortsby, the protagonist of the story, is out at this time of night as well.)
When Norman finds error with the story of a young man in need of money, the reader comes to understand the "type" of people who are out at dusk. As the story goes on, Norman comes to find out that the young man had lost his soap and Norman proceeds to loan the young man money.
It is not until Norman comes across an old man whom he had seen earlier in the night that he (Norman) comes to find out he had been deceived. (The soap he found was not the young man's; instead, the soap belonged to the old man.)
Norman (prior to coming across the old man) states "It's a lesson to me not to be too clever in judging by circumstances." After finding out about the true owner of the soap, the reader is left with the sense that one's first perception of another is normally correct. Norman should have stuck with his instincts about people who come out at dusk. He was deceived by the young man by his own critical mind. If Norman would have kept his original thought on not trusting the young man, he would not have been deceived. The "appearance" of the soap simply justified the young man's story. The soap appeared to have belonged to the young man. When Norman comes to find out that the soap was the old man's, he realizes that things simply are never as they seem.