"The customer is always right" is just being misinterpreted by people that don't know better. It's a figure of speech in business theory, referring to a scenario where you have a product you think should sell, but somehow it doesn't. It means that if the customer doesn't want to buy your product, then it doesn't matter how to spin it or what your analysis is: Their judgment is ultimately the only one that matters, because you depend on them to buy what you sell. You don't make any money off of being right if the customers don't agree. People have taken that out of context to mean that whatever a customer says is automatically correct. And that's not the case at all.
"The customer is always right" is 100% true, and an extremely important lesson to learn for any businessperson. But it doesn't mean what Joe Average think it does. And the commonly used meaning is complete and utter nonsense.