Amazing, isn't it, just how often PCOs simply go and look at what the client says is the problem. A good PCO will look around the area and extend that inspection. A really good PCO will go vertically and check product movements as well.
Where does that hole go?
Are they really coming in under the door or is there a source inside the building?
How often is the baiting/trapping system checked, but no real effort put into looking for droppings, footprints in dust, smear marks, or other telltales of mouse activity
It is remarkably seldom in my experience that a mouse problem in a building will be associated with a gap below a door. Mostly, it is due to an established population (which can be 2 to 200) living inside the building. It is our job to find out where they are, and not just assume the seemingly obvious.
Occam's razor is sharp - and can cut you!!