How do Mr. Shiftlet and Mrs. Crater attempt to exploit each other in "The Life You Save May Be Your Own" by Flannery O'Connor?

Mr. Shiftlet exploits Mrs. Crater's overwhelming need to provide herself with a caretaker for her property and a husband for her deaf and dumb daughter Lucynell. One of the first things Mr. Shiftlet notices on Mrs. Crater's property is the Ford automobile in the shed. His "sharp glance" seems to be drawn to the car in the opening section of the story. He even claims he can fix the car if Mrs. Crater will allow him to do so. Once the car is running, Mrs. Crater offers Mr. Shiftlet the automobile, her daughter, and the property upon her death, if Mr. Shiftlet will marry Lucynell. The two bargain over Lucynell like she is a piece of property. Ultimately, Mr. Shiftlet agrees to the marriage. Both seem to get what they want, but Mrs. Crater underestimates Mr. Shiftlet's need to wander. He simply uses Mrs. Crater and Lucynell to obtain a car, the means to continue his drifting.