Not only should you be making amends and solving problems, but also turning these "problem customers" into raging evangelists.
In most companies, the customer service department is seen as a necessary evil. With a low goal of simply meeting customer expectations, these companies miss their real goals by a sizable margin and prevent customer from becoming "sticky," which should be the goal of every employee. Why do so many companies view the customer service mission as only minimising negatives rather than a significant opportunity to foster long-term relationships? Not only should you be making amends and solving problems, but also turning these "problem customers" into raging evangelists. It is possible to accomplish these objectives with a few changes that should be championed by senior leaders and your team can institutionalise.
If you are carefully listening and acting on negative customer feedback, surveying customers regularly to anticipate their changing needs, and letting them help you tell your company's success story, then you will find these investments in customer service will pay dividends and increase customer stickiness.