What does Mrs.Hopewell mean by the phrase "good country people"?
"Good country people" refers to those whom Mrs. Hopewell sees as simple and moral. They are the opposite of how she views her own daughter, Hulga, who revels in her nihilism and uses her education to demonstrate her supposed superiority. The "good country people" are seen as innocent, as opposed to the experience that Hulga imagines herself to have, and the experience that Manley Pointer actually has.
Many of O'Connor's stories deomnstrate irony in the title. This story is no different. Hulga seeks to tempt and corrupt Manley Pointer, seeing him as a simple Bible salesman. Yet he turns out to be more corrupt than she could imagine. He steals her leg, & when she pleads, “Aren’t you just good country people?” he replies, “I hope you don’t think that I believe in that crap! I may sell Bibles but I know which end is up and I wasn’t born yesterday and I know where I’m going!” Thus, the "good country people" turn out to be a lie.
When Mrs. Hopewell refers to others as "good country people," she means it as praise for people who are "simple" and "the salt of the earth." O'Connor uses this dialogue ironically, however, because Mrs. Hopewell only uses this phrase to describe people she considers to be inferior to herself. Mrs. Hopewell not only calls the Freeman family--her hired help--good country people, she also uses the term to describe Manley Pointer, the Bible salesman who comes to her door. Neither Mrs. Freeman nor Manley is entirely what they seem, so Mrs. Hopewell's labels ultimately look ridiculous.