Killing moths requires a pesticide licence in most states. You may be committing a crime to sell that service.
The pesticide can be harmful to the rug. Be careful,e specially if the customer may be sensitive to chemicals.
Two ways to treat. #1 is by freezing. Needs to be lower than 20 F for a couple days. #2 is to call a licensed exterminator.
The moth products for rugs are to keep moths away so they don't lay eggs on the rugs. They do not kill the moths or the larvae once they get in the rug.
Keeping a rug clean, in use and some light on it are all ways to help keep moths away. Don't store a rug that is dirty. Even rugs in rooms that are not used often should be cleaned every 18 months or so.
If there are moths in one rug, likely they are in every wool rug or garment in the house. So, check the other rugs. They may need to be cleaned and/or treated as well.