"Customer is always right" is one of the idea employed by some of the company in the market. There is nothing right or wrong about the idea. It was based on the intention to fulfill and satisfy customer needs. However, this can be achieve by not bound with the mean of the phrase "Customer is always right". but with what we can do to help customer and our own company to achieve the most practical benefits.
As a salesman I can find many instances of when the customer is NOT always right, but to build up a rapport with the customer I must act as if the customer IS always right.