You sound like a breath of fresh air in the housing rental market.
My cousin is the same. He rents out two properties and is a damned good land lord. Never overcharges. If anything, he undercharges.
We had a great landlord in London. She never increased the rent in 5 years, which was pretty low anyway for a flat nr Wimbledon with a garden and near a couple of tube stations, and she sent our deposit back as soon as we left with no deductions for carpet cleaning and all that bollocks. If anything needed fixing, she'd send a tradesperson round no quibbles or corner cutting. When the new tenants moved in, she only increased it by £50. She just wanted good tenants.
Similar when we lived in Plymouth where we had a two bed flat, with coastal views of Plymouth Sound and Drake's Island, and near the old town/harbour (Barbican), for £600 a month. I saw it listed the other year and they must have sold it as it's been refurbished but with the rent more than doubled.