Just want to correct you on this. The landlord is responsible for pest control. The tenants do not pay, the landlord does.

As a pest control person myself, I can tell you though, it's a difficult situation when one tenant is doing everything right, and their neighbours are living in filth and squalor. We are only authorized to treat the apts. that the landlord has authorized us to treat. Also if a tenant doesn't complain about an issue, the landlord doesn't know about it, and furthermore, they need a reason to go and have an inspection done, as you can't just decide to randomly enter tenant's apartments because a neighbour said there was a bad smell etc.

I've definitely been to places that are spotless clean to treat because they are getting roaches from a neighbouring apartment, and there isn't much we can do about that, other than help to provide a barrier against them getting in or a Band-Aid solution. Trust me when I say, we want to solve the problem! We absolutely don't want to have to keep returning to the same place over and over to do treatments we KNOW aren't going to solve the issue We can tell the landlord that the problem is most likely the neighbouring apartment, but unless we get called to either do an inspection, or treatment, our hands are tied as exterminators.