Exclusion first, because bait alone is a treadmill
A building with an open route in will keep receiving rodents no matter how much bait sits in it. Killing the ones inside empties the space, and the space refills from the same route, which is why a site on permanent baiting with no proofing is paying a subscription rather than solving a problem.
So the survey looks for the way in before it looks for a station. A young mouse passes a gap the width of a pencil and a rat a gap the width of a thumb, so the candidates are door sweeps, service penetrations, weep holes, damaged drain covers, roof junctions and the gap where a shutter meets an uneven floor. Where the fix is a building work rather than a pest work, the report says so.

