In The Adventures of Huckleberry Finn, the king uses the common people's religious emotions to dupe them and steal their money. Can you think of some other examples from American literature of characters who defraud creduluous Christians out of their money or abuse their trust?
Flannery O'Connors story, "Good Country People", plays on the themes of fraud, credulity, and Christianity. In this story the less than credulous Joy is duped by a young man who she is trying to manipulate and who she initially believes is a "credulous Christian".
The young man is not as simply minded as he makes himself out to seem and he, ultimately, turns the situation to his advantage, robbing and degrading Joy.
In a different way, Arthur Millers's The Cruciblealso fits this description. In that play a group of young women play upon the town's credulity and also play specifically on the town's doctrinally-driven paranoia regarding witchcraft.