A rat in the stockroom is never one rat
For a grocery, a café or a warehouse, the first rat you see is the one that got careless. What the sighting actually means, and what to do in the first day.
Rats are careful. They move along walls, at night, and they do not cross open floor unless they have to. So the rat you saw at eleven in the morning, in the middle of the aisle, was not the first one in. It was one of many, and it was out because the others had the good spots.
What the signs mean
Droppings along a wall line mean a regular run. Gnawed cartons at the bottom of a pallet mean they are nesting close by, probably under it. Grease marks on a wall at knee height mean the run is old. A smell of ammonia in a corner means a nest. Any one of these is enough; you do not need all four.
What to do on day one
Do not put poison down yourself in a food business. A rat that dies in a wall cavity is a worse problem than a live one, and loose bait near stock is a liability. Move stock off the floor where you can, note where the droppings are, and call. A baiting programme with tamper-proof stations and multi-catch traps, placed where the runs actually are, clears a stockroom without either of those risks.
Why a programme, not a visit
A grocery or a warehouse takes deliveries every day, and every delivery is a chance for a new arrival. One treatment clears the current population; a regular check keeps it cleared. The rodent control page explains how we set one up, and the commercial page covers the rest of the building.