Manley Pointer is successful in his misadventures of "Good Country People" because he taps into the weaknesses of the people whom he exploits, pretending to commiserate with them on their beliefs.
Pointer first identifies Mrs. Freeman, who "could never be brought to admit herself wrong on any point" as extremely narrow-minded. When he arrives under the pretext of selling her a Bible, Manley examines the parlor into which she has invited him and observes that there is no Bible. After Mrs. Freeman responds that she keeps hers at her bedside and tries to dismiss him with her need to attend the stove, he remarks, "People like you don't like to fool with good country people like me!" This, of course, elicits an immediate reaction from Mrs. Freeman, who prides herself on being just that--a good country woman. Pointer, then, flatters her with being an honest person. Then he says he has a heart condition, and this taps into her sympathies as her daughter has the very same health problem. He has won over Mrs. Freeman.
When Mrs. Freeman asks him to stay for dinner, Pointer accepts; while he eats he observes Joy. Before he departs, Mrs. Freeman observes him as he says something to Joy/Hulga and then gestures with animation. From this brief conversation, he has probably recognized her arrogance that presents a vulnerability which he later exploits.
He has invited her to meet him at the gate the next day. At first, Hulga thinks of this meeting as "a joke," but then she imagines
...dialogues for them that were insane on the surface but that reached below to depth that no Bible salesman would be aware of. Their conversation yesterday had been of this kind.
He has told her that he felt that they were meant to meet and that he is dying. Giving her "a dying look," he has begged her to meet him. In her blind arrogance, Hulga considers seducing Pointer and then, as a PhD. and his intellectual superior, she plans to work his remorse afterwards into a deeper understanding of life, thus taking his shame and turning it "into something useful" like her nihilism.
However, Manley Pointer, whose name has phallic connotations, assumes a dominance in their encounter by playing into her arrogance. When he acts as though she is too crippled to climb into the loft of the barn because of her artificial leg, Hulga's pride is insulted and she immediately climbs up there. Once there, he seduces her knowing that she is probably sexually inexperienced. Testing her, he demands that she say she loves him, but Hulga retorts that she has no illusions; further, she determines mistakenly that he is truly innocent. Thus deceived in the same manner of her mother, Hulga is also vulnerable, and Pointer exploits this by asking her to remove her artificial leg. Doing so, Hulga then becomes completely "dependent upon him."
Her brain seemed to have stopped thinking altogether and to be about some other function that it was not very good at.
Indeed, Manley Pointer is a consummate salesman, easily reading people and tapping into their weaknesses.
Manley Pointer has conquered her intellectual pride by exploiting her arrogance and manipulating Hulga to put herself into such a vulnerable position. He mocks her, "...you ain't so smart. I been believing in nothing ever since I was born!"