Interview Question for Merchandiser at Hudson's Bay:

Best case scenario.
Speaking calmly to the irate person, Listen first. Find out what their issue is.
What does the person want you to do to "fix it"? Offer alternatives and let them make the decision. Exchanges, returns, discounts.

Try to understand how they feel (even if they are unreasonable). Show sympathy and interest in their problem. Try to lighten up the conversation to more neutral ground. Keep your voice even and friendly. If need be, apologize on behalf of the company, remember to say thank you and still encourage them to come back again. Most people will respond if you are pleasant.