REMEMBER: THE CUSTOMER IS ALWAYS RIGHT
Acknowledge that the customer is upset and ask them to tell you the problem. Listen carefully, and if you think it will help, rephrase their complaint to make it clear that you understood what they said. Sometimes an unhappy customer just wants to be heard.
The old "customer is always right" philosophy may still be the best approach for dealing with obnoxious shoppers. Customer service experts have long said that a happy customer tells one or two friends, while an unhappy customer tells several—or in the age of social media, hundreds of his closest strangers. And these statistics can be magnified by the emotions related to holiday shopping.