Tenant deducted rent for volunteered work

[Cat R.]

I have a renter who decided to pay himself the rent value for helping to fix a plumbing leak. My father took a few guys with him to work on the piping and wall plastering on one of the houses. The tenant of that residence offered to help and told my dad that he doesn’t have to pay him just give him whatever he feels his work is worth if he wants. Come rent time, he told my dad he was paying himself December’s months rent!!