“The customer is always right” is a terrible phrase that haunts those in retail. Anyone who has ever worked retail (or hospitality or in fact anywhere that is public-facint) knows that the customer can be not just wrong but downright unreasonable.
What is important however is that you resolve as many customer issues as possible. Nowadays your customers have access to The Internet and a righteously indignant (former) customer can smear your brand up one side of the Internet and down the other. And if you don’t treat them with respect and generosity then this could happen to you:
http://www.youtube.com/watch?v=5YGc4zOqozo&feature=channel_page
On a side note: if you’d like help creating an Internet presence as a lens for your negative experience we can help with that too 