When I got my first BTL, the first few years were issue free re damp.
New tenants moved in, young couple, after a few months they advised of damp in the bathroom. I visited, sure enough, signs of black mould and damp.
I asked if they ensured the bathroom was well ventilated e.g. after baths, showers etc. The guy worked late in a restaurant and liked to have a shower when he got home. He also advised me his partner had some sort of condition whereby she didn't like the windows open i.e. no drafts or breezes. So, frequently, the bathroom window wasn't opened, indeed none of the windows were.
I advised re importance of ventilation, wiping down surfaces etc. I printed off and gave them a one pager advisory re how to keep on top of it. The guy messaged me x weeks later to say the tips were working. He thanked me for the advice, stating this was their first place and they didn't know about stuff like that.
They've been out for years. Since then, latter tenants have reported no issues with damp. Funny that
p.s. for the usual suspects who are gearing up to reply, let me save you the bother. Are there properties that are damp through no fault of the person living there? Yes. Are there landlords who rent out such properties? Yes. Are there landlords who do nothing to assist tenants as I did above? Yes.
However in many cases, the issue isn't the property itself, it's the people living there and how they live. Fact.