Great customer service in the janitorial industry involves many moving parts. It is important to listen to the customer, apologize for any concerns, solve their issues, and thank them for bring the item to your attention. Above just this, I believe that great service is channeling your service to the individual needs of each client. 

Ask the client what their expectations are ahead of time and continually ask them if they are satisfied with their service and if they would change anything. Explain how important an open line of communication is.