When you deliver a quality product and still are challenged with an unhappy customer, at some point in the customer process the customer wasn't satisfied. It is at that moment the customer formed their impression of how good you are. The customer does that through their definition of their experience. That is defined by the quality of presence from the person who is standing in front of them. Remember, they want to feel good about their experience.
Organization is designed to take care of their needs.
Two of the most common destroyers of businesses are inconsistencies and inefficiencies. Each of these punish the customer. Each of these create confusion and leave the customer frustrated. When they are paying money for a service and exit frustrated, I don't care how great your quality is they will not be satisfied. Manage the moments of touch .