Chapter four of John Steinbeck's The Pearl explains a lot about how the priest and the pearl buyers control the town, or at least manipulate Kino's people. 

The priest does his part by scaring the villagers into doing their business (i.e., selling their pearls) in town rather than going elsewhere and trying to get a better price. Kino relates a story which the Father told about someone who tried to do that and brought down a punishment on himself. Now the priest calls it a sin to take a pearl elsewhere to sell. Kino relates the analogy which the priest gave them in a sermon once:

"[E]ach man and woman is like a soldier sent by God to guard some parts of the castle of the Universe. And some are in the ramparts and some far deep in the darkness of the walls. But each one must remain faithful to his post and must not go running about, else the castle is in danger from the assaults of hell."

Clearly the church's interests (okay, probably just the priest's own interests) are best served when he convinces the pearl sellers to keep their business in town; the pearl seller no doubt gives the priest and/or the church a kickback for doing this.

Though there seem to be many pearl buyers in town, there is really only one, and they all work together to get the best (lowest) price for the one buyer. 

It was supposed that the pearl buyers were individuals acting alone, bidding against one another for the pearls the fishermen brought in. And once it had been so.... Now there was only one pearl buyer with many hands, and the men who sat in their offices and waited for Kino knew what price they would offer, how high they would bid, and what method each one would use. 

It did not used to be this way. Once the villagers gave all their pearls to one man who took them to the capital to sell; now, however, the priest and seller use intimidation to keep all selling local. Obviously this is a power play by both the priest and the pearl buyer to cheat the villagers and get more for themselves. The legal term is "collusion" and it is not an acceptable business practice; however, the villagers are too powerless, to afraid, and too naive to do anything other than what they are told.

Of course, by the end of this chapter, Kino is so infuriated at the unfairness and futility of trying to sell his pearl that he storms off to sell it elsewhere. The pearl buyer and his "hands" know they played too hard, but it is too late.