The presence of rodents in man's environment was first documented in the 7th century. Those most likely to affect your commercial environment are:
Also known as the brown rat or sewer rat, this stocky rodent burrows along building foundations, under rubbish & wood piles, and in landscaped areas. The Norway rat generally remains on the ground floor when he penetrates a structure.
Also known as the black rat, this rodent is smaller than the Norway variety. This rodent is a climber, so it can access a structure via open vents & pipes on the roof. It is most commonly found climbing vegetation, in a crawl space or a false ceiling, or on a shelving unit.
This rodent is much smaller than a rat, yet a young rat might be confused with an adult mouse. Keep in mind that a mouse's feet and head are disproportionately larger than its body.