Talk to them
I am trying to see what can be done about this rather unusual situation right now. A woman wrote in to say that she had a friend who was upset about some cats that were defecating in his stairway. He said the town council wasn't doing anything so he called pest control himself.
She went down and spoke to the woman who seemed to be looking after the cats. The cats were sleeping on a sofa outside the woman's flat on the third floor. The latter denied they were her cats, but it is likely they are probably are. The woman with the cats also said that if they came and took the cats away, then they should go ahead and do so. She asked the woman who wrote in to take the cats away if she wanted them.
I told the woman who wrote in that we need to do this from both angles - we need to speak to her friend, and we need to try and reason with the woman. However, the woman wouldn't let us talk to her friend, and she was afraid to approach him as well. She said he would not be amenable to this. She asked if the cats could be taken away instead as she didn't want them killed.
Now I don't know her friend, and perhaps he really does have a bad temper, BUT the easiest way to stop them being killed is to tell her friend to cancel the pest control coming down. I explained TNRM to her, explained the vacuum effect, and why removing the cats wouldn't solve her friend's problem anyway because this woman would probably just take some more cats home.
She listened to me, but was worried about getting involved and would need to think about it for a while.
I notice that in a lot of mediations we do and the like, the problem is that people just don't talk to each other. As SK wrote in a comment earlier, he wondered how many people went straight to the town council. In this case, it's worrying that a woman felt she couldn't even talk to her friend. A lot of people say that they don't want to cause bad blood, but in my experience, the thing that causes the MOST ill feeling is that people cannot understand why a third party was called in. Many people ask why the neighbours just didn't come and tell them directly they have a problem.
So if there is a problem, try talking to your neighbour - I've blogged about it before, but it is important. We do need to stay on good terms with the neighbours due to the cats - and I know there are some very unreasonable ones. However, most neighbours will probably cut you more slack because you've spoken to them and they know you. It may also encourage them to come to you before going to the town council.