The title points to the theme and style of Flannery O'Connor's story. O'Connor is known for her realism that veers into symbolism, and this story is no exception.
The grandmother is the type of Southern woman who believes in social decorum and being a "lady," even as her family falls down the social spectrum. Saying a "good man is hard to find" is a way to convey one's own higher status against a world of deficient characters. Others do not meet one's refined sensibilities, both in status and in morality. Good thus has a double meaning, and despite her pretension the grandmother falls short on both measures.
The title comes into play when the family stops to eat and the grandmother speaks to Red Sammy:
"People are certainly not nice like they used to be," said the grandmother.
"Two fellers come in here last week," Red Sammy said, "driving a Chrysler. It was a old beat-up car but it was a good one and these boys looked all right to me. Said they worked at the mill and you know I let them...
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