Rodent activity is a bad sign. I use the U.S. Armed Forces’ defense readiness condition (DEFCON) as a scale. Any rodent presence is a serious issue, but I consider rats DEFCON 1-2 (the highest levels) as compared to mice, which are more like DEFCON 3-5. Price your agreement on the DEFCON level: The more intense the level, the more work and maintenance needed.
You can be the hero solving a rodent issue. You will have a customer’s loyalty for life. Use an integrated pest management (IPM) program with a focus on exclusion first. When using snap traps, place the trap where the kickplate faces the wall.