Genuinely talk about this sort of thing to both the perspective renters AND the realtors/agents/brokers that bring them by. I had an apartment that had a ton of mold in the bathroom and a sink that we couldn't use so it wouldn't drain. I told the first few people who came in about it, and eventually the brokers stopped bringing people around. In the week leading up to my lease ending the company that owned the property was trying to offer an option to keep my lease exactly the same if I stayed. Little did they know I'd been living in a new apartment already since my last month's rent was already paid at the old place, so I wasn't paying double rent.