Customer service is meant to be improved on as often as it can be. Customers behaviour is always erratic which is why your customer service should be adaptive to make up for how your customers behaviour impacts on your business.
The thing that I have come to understand about customers is that they are never truly satisfied all the time which is why they always keep asking for improvement on services and products that they have purchased from any company.
I believe it is the reason why getting into feedback system with your customers is always very necessary so that you will not be thinking everything is okay with them when they are already not happy about your business.