Рассказ Сомерсета Моэма "Mr.Know-All" - Мистер Всезнайка.This is also an old story, much anthologised.
This setting is a shipboard. There is an assortment of travellers cruising from the US to Japan. Among them is Kaleda, a fellow who brags that he knows everything and that he can never be wrong.
The narrator dislikes him for his breezy manners and for his cocksureness.
There is the inevitable cardgame and during one session Kaleda bets that the pearl necklace that an Ambassador’s wife was wearing was of high quality. This is disputed by the diplomat who says it is an imitation jewellery.
Kaleda discloses that he is in pearl business and ought to know. He then bets an amount and asks the lady to unfasten and give the necklace for him to examine.
Did he win the bet or not?