Describe the personality of the first pearl buyer. What does his trick with the coin represent?

The dealer is flipping the coin in his hand as if he was performing a trick of illusion. These dealers care nothing for Kino. They make their living short changing people to make a profit. His trick with the coin suggests that his dealings with Kino are based on smoke and mirrors so he can take advantage of Kino,

"the buyer's eyes had become as steady and cruel and unwinking as a hawk's eyes, while the rest of his face smiled in greeting. And secretly, behind his desk, his right hand practiced with the coin." Like the doctor, the pearl buyer is only interested in taking advantage of Kino.