A bodged supply will nearly always put the occupant at risk, so your duty of care is to the preservation of life and property first and foremost.
Secondly, it's a criminal act is it not ? so your duty as a citizen is to report the crime.
Thirdly, it's a moral issue. Why should the cheeky beggars be able to get away with not paying their dues ? I have no sympathy for people like that. Theft is theft, whether it be meter fiddling, ripping out railway cable, armed robbery, or investment banking. Screw em.