The tone of the story is ironic and mocking. As she often does, O'Connor simply gets inside the head of her main character or characters and conveys their thoughts in a deadpan, mocking, scathing way. For example, she mocks Mrs. Hopewell's mortifyingly condescending and self-satisfied attitude about her own superiority in the following sentence. O'Connor simply lets Mrs. Hopewell hang herself by relaying her smug thoughts without comment:
Mrs. Hopewell liked to tell people that Glynese and Carramae were two of the finest girls she knew and that Mrs. Freeman was a lady and that she was never ashamed to take her anywhere or introduce her to anybody they might meet.
A reader might want to squirm and blush at the thoughts Mrs. Hopewell is proud to tell people about and at her unthinking assumption of the right to pass judgment on and be the "superior" social conduit for the Freeman family, but O'Connor's deadpan tone never blinks.
As we can see, O'Connor mocks Mrs. Hopewell's blindness, vanity and petty need to feel superior. Mrs. Hopewell labels Manley Pointer, the Bible salesman, "good country people," because he seems to be a polite country bumpkin who bows and scrapes to her. It never occurs to her to question this facade.
O'Connor is also deadpan and dryly ironic about Hulga, who believes she is so sophisticated, worldly, and intelligent because she has a PhD. She too feels superior to Manley only, ironically, to be easily bested by the seemingly simple and "backward" salesman who she assumed she would seduce and control.
For a long time, I saw Manley as wholly evil—and he is deceptive, mean, and spiteful—but he also is more honest about who he is than either Mrs. Hopewell or Hulga. He doesn't delude himself that he is "good people."
O'Connor moves to a tone that mixes sincerity with scathing revelation near the end, signaling with the sunlight that Hulga has had her awakening:
And I'll tell you another thing, Hulga,” he said, using the name as if he didn't think much of it, “you ain't so smart. I been believing in nothing ever since I was born!” and then the toast-colored hat disappeared down the hole and the girl was left, sitting on the straw in the dusty sunlight.