what are the surprise ending of the story 'Dusk' by Saki?

Gortsby believes the young man is lying and is trying to
con him out of money.  He believes himself a good judge of people, and, after listening
to the young man's story, confronts him with the fact that he didn't have the bar of
soap he says he bought.  The young man, pretending to be surprised that he didn't have
the soap, runs off --- supposedly in search of it.  Then Gortsby finds the soap
underneath the bench.  He feels bad for having misjudged the young man and goes in
search of him.  He finds him, apologizes, and gives him some money.  However, he expects
the money to be returned and gives the young man his card.  When he returns to his
bench, the old man who had been sitting there before the young man came was searching
all over the ground.  Gortsby asks if he has lost something, and the old man replies
that he lost a bar of soap.  The surprise ending is that the young man really was
conning him, and the very bar of soap that he thought proved the young man was a con man
was the reason he ended up giving the young man some money.  Gortsby still got
conned.