what evidence is there that tom and his wife are always fiting

From the text:

He had a wife as miserly as himself; they were so miserly that they even conspired to cheat each other. Whatever the woman could lay hands on she hid away; a hen could not cackle but she was on the alert to secure the new-laid egg. Her husband was continually prying about to detect her secret hoards, and many and fierce were the conflicts that took place about what ought to have been common property.