Smell only
Smell, nothing to point at
Worth a visit from the Detroit line when the smell points at a space a person can enter. Not worth one when it is a mouse in a sealed plaster wall. Tell the difference below.
Points at a reachable space
Strongest at the basement stairs, the attic hatch, the garage door, the enclosed porch. Flies at one window. Scratching a few weeks ago that stopped. A vacant unit where the last tenant left the back door open. All of those are a recovery job.
Points at a sealed wall
A faint smell in one interior wall of a plaster house with nothing else going on. For a suspected mouse or rat inside an inaccessible wall cavity, opening the wall is often not the first step. If the carcass cannot be reached without cutting into the structure, the odor will typically lessen as decomposition runs its course. Nobody should sell you a visit for that.
Before you call anyone
Run water in every drain, including the floor drain in the Michigan basement. A dry trap smells like something died. Check the furnace return. Then call.
Multi-unit
A smell in a hallway or shared wall of a building is often a shared void or a common-area space. Say which units and which floor, and who has the keys.
Where it ends
Usually a reachable space, which is the building page. Sometimes outside against a foundation, which is the lot page. Pricing covers why a search is quoted differently from a pickup.