A great pest detective.
I have used Randy of Nature First Pest Control twice. Once in my old home, and again recently in my current house, which is fairly new. I was having trouble with what I thought was mice in the crawl space. I had tried other pest control companies with no luck, but Randy was the guy that finally solved the mystery.
There actually were mice in the crawlspace, hiding in a pipe that was under some landscaping fabric. No one else bothered to look under the fabric. Randy sealed up the ends of the pipe, which wasn't exactly a complete fix, but he did identify the problem area. I would have liked the fix to be little more thorough, but Randy is very good at detecting things. I hesitate a bit in recommending him, because he is more expensive than the others, but if nothing else is working he is a good last resort.