In the case of positive feedback, the listener understands why and how his actions make an impact. In the case of negative feedback, he understands how he might be hurting the enterprise. By linking behavior and consequences, you're giving power to the individual. You're helping her realize that her actions mold what happens around her each day. The Ah-ha Experience.
Great feedback is educational.
The listener learns not only the consequences of his actions, but alternate ways of doing things in the future. By learning an alternative repertoire of behavior, she becomes a more effective member of the team. Now you should be better able to respond to these customers. But good feedback is usually best delivered in a cordial, professional tone. Measured comments, without a lot of emotion, place the listener at ease and set the stage for effective coaching in the future.