Why does Mrs. Crater think she has nothing to fear from Mr. Shiftlet at the beginning of "The Life You Save May Be Your Own" by Flannery O'Connor?

In the opening paragraph of Flannery O'Connor's short story "The Life You Save May Be Your Own," the third person omniscient narrator notes that Mrs. Crater did not fear the one-armed "tramp" who approaches her house one day at dusk. The fact that he has one arm makes Mrs. Crater believe he is basically harmless. She has probably also had several experiences with men wandering onto her property looking for work. She seems to know...

In the opening paragraph of Flannery O'Connor's short story "The Life You Save May Be Your Own," the third person omniscient narrator notes that Mrs. Crater did not fear the one-armed "tramp" who approaches her house one day at dusk. The fact that he has one arm makes Mrs. Crater believe he is basically harmless. She has probably also had several experiences with men wandering onto her property looking for work. She seems to know immediately how to deal with Mr. Shiftlet by offering him meals and a place to sleep if he will work for her. She knows better than to let on that she has any money to pay him.

Obviously, Mrs. Crater underestimates Mr. Shiftlet's intentions and his ability to manipulate her into giving up her car. In the end, it seems that Mr. Shiftlet fixes up the property and treats Lucynell with kindness for only one reason: he wanted Mrs. Crater's automobile to continue his drifting. At one point, Mr. Shiftlet even concedes that his nature is that of a drifter. He tells her that a "spirit" is "like an automobile: always on the move." In her desperation to attain a son-in-law, Mrs. Crater allows Mr. Shiftlet to marry Lucynell and take the girl and the automobile on a honeymoon. Mr. Shiftlet eventually dumps Lucynell and steals the car. A man Mrs. Crater believed to be harmless ultimately puts her daughter in danger and takes one of her most valuable possessions.