What does the fact that Michael would sell his wife tell us about his character?

Michael feels that his marriage at a young age rotted any chance he had of living decently, while Susan is soiled by the fact that her husband would sell her as he would sell a horse. Oddly, at the time, selling one's wife was not an uncommon occurrence. Although Michael is portrayed as largely a sympathetic character, selling his wife was a pretty low thing to do.