My late DP was renting when we first got together. His LL lived just round the corner and used to let himself in when tenants were out. He had 14 flats on that site and 2 other huge houses split into several flats.
Then he used to snoop. He would read tenants' post and paperwork and gossip about them to other tenants, we knew how much DP's neighbours earned, that one was getting divorced, another had MH issues and all sorts.
He thought it was acceptable to simply disable the shower when it started leaking and causing damp on the adjoining wall, causing damage to the stairwell. He only fixed it when DP complained that the bath was virtually useless because the water tank was so tiny you could only get 3 inches of hot water in it. DP had no functioning oven for more than 2 months, he wouldn't do anything about pigeons nesting under the eaves (you couldn't leave windows open on hot days because the fuckers came in and shat everywhere), he gave DP the keys to an empty flat so he could use the washing machine in there while he was waiting for the LL to fix his, which took 4 months, he put the rent up loads because I stayed there 4 nights a week and he felt it was fair, he wouldn't let tenants change energy supplier, the meters were wrongly labelled and DP was paying another tenant's bills for over a year (that took 3 months to sort out), he decided visitors had to park on the street after he turned up and found he couldn't park close to the front door, then issued a diktat that visitors must not park within 20 yards of the entrance on the public highway, and he decided that tenants should not have children under 14 to visit.
The worst was him telling us, quite proudly, that he wasn't renewing another tenant's agreement because she had a black boyfriend and he didn't "want that sort in his properties".
He had bought several very big old houses in the 1960s. DP and I invented a whole backstory where the LL had been a professional criminal who had got away with a massive robbery and had used the proceeds to buy the houses!