In Steinbeck's The Pearl, the pearl buyer who practices "sleight of hand" with the coin is setting the mood for this chapter, in some ways providing foreshadowing.
The use of sleight of hand is practiced to entertain or to trick. The movements are so quick and sure that an observer cannot keep up even when watching closely.
In that all the pearl buyers are employed by one man who is extremely "tight fisted," it is no surprise that Kino is not going to be dealt with fairly. When the first pearl buyer tells Kino the pearl is too big, and therefore worthless, Kino refuses the low offer the man makes and moves on to the next pearl buyer.
As each man makes the same observation and offers the same low price to Kino—insisting that his pearl is worthless—they are trying to trick him. It is their hope that Kino will become discouraged and sell just to get some money.
Kino is aware of what is happening, that they are trying to cheat him. He announces that he may take the pearl to the capital to get a fair price, and he leaves.
Trickery displayed at the start of the chapter prepares the reader for trickery against Kino has he tries to sell his beautiful pearl.