I don't think there is a bigger fallacy in business than the concept that 'the customer is always right'. The customer is frequently wrong, but the skill that comes into it is being able to tell the customer that they are wrong without losing them as a customer. Of course, there are the (rare) customers who will not see reason no matter how it is presented to them and these are the ones you need to cut loose as a consultant, no matter how much it goes against the grain.

The only sense in which the customer is always right is in the broader sense of the word 'customer' that means the market. If you have a service or product that is not selling, it is not because the customer is wrong, it is because you have the wrong service or product, or because you have not communicated the benefits of what you are offering well enough. That was the original meaning of the saying, but it seems to have been corrupted to mean that every individual customer is always right, which is clearly ludicrous.