Despite some leftists having declared the real estate companies as their main enemy in Germany imo they aren't that bad. You have to pay the market price and are dealing with professionals. One of our former tenants has also accused my grandfather of some bogus numbers / having stolen oil for himself which was nonsense. Imo it's not only a bad thing to have a private landlord as a tenant but it's also a bad thing to be a private landlord.
I'm not trying to imply all landlords are bad. My current landlord is great and I've had great landlords before. (One ended up in jail though, but hey. You win some, you lose some)
I'm accusing this landlord of fraud because he is committing fraud. Objectively, provable fraud.
Also, I have no problem with paying the market price; this guy however, had problems with the market price itself, so he increased it arbitrarily, violating many rental and tax laws.