The name Shiftlet implies that he will shift, or that he is shifty. Each of these is true.
Mr. Shiftlet’s name has a double meaning. On the one hand, it could mean that he is shifty and not to be trusted. A shifty person is immoral or sneaky. Mr. Shiftlet’s behavior can be interpreted this way. When he arrives on Mrs. Crawford’s farm he talks about God and does not seem to care about money, but by the time he leaves he has taken her car and conned her into giving him money to go to town to marry her daughter.
Another interpretation is that Mr. Shiftlet really was who he seemed to be in the beginning, but he shifted. He might have not been a conman, but a moral man. Her influence corrupted him, and the longer he was on the farm the less moral he became. Mrs. Crawford is clearly immoral.
"How old is she?" Mr. Shiftlet asked casually.
"Fifteen, sixteen," the old woman said. The girl was nearly thirty but because of her innocence it was impossible to guess.
She lies about her daughter’s age, figuring that since she is mute and unspoiled it won’t make a difference. In the end, he agrees to marry her, but only if she pays for the wedding. This can be taken either way. It can suggest that he really does want to marry her but actually has no money, or it can suggest that he is asking for a bribe.