Describe the pearl buyers trick to get the lowest price

The Pearl dealers actually act in collusion. In practice they all work for one dealer. They try to get the best price for their boss. By doing this, the pearl traders ensure the cheat the already poor fishermen out of their meagre earnings from the small pearls they catch. The first pearl dealer pretends the others are acting independently and are in competition. All of them pretend that Kino's pearl is worthless.