Re: Campaign Idea . . . almost.
I too was thinking along the lines of plumbing/construction but the Pest Control would work best I think.
My reasoning is same as the others above, it covers them moving around to new places around the city/county, old and new buildings, etc. The evacuation excuse is a bonus.
And like someone mentioned, rats are the cause of alot of hauntings, so many plot hooks there.
The problem I see with a bar or Stop-N-Rob (conv. store) is that you have to stay put and wait for trouble to come to you and then go hunt it etc. The OP said that the PCs didn't want to look for trouble, it just found them.
Now that's no reason they can't hang at a bar that has troubles, think Cheers with issues or make friends with a store clerk (they have to go somewhere when they get the late night munchies), ie they stop in and stock up on snacks on the way to a job and maybe he drops some hints on a job for them. Unfortunately for them, he really is a certified Freak Magnet....