Is the customer "always right" , or it's an old saying?

The customer is king.
But some kings were beheaded … I would equally say that the customer might always be right, until he gets really wrong.
Seriously, each and every customer’s request should be considered with attention, and one should do everything possible to serve the customer’s needs.
The trouble starts when the customers don’t express their “business need”, but request something they believe would help addressing this business need.
And go wrong because they’re not experts in this specific field.
Did it ever happen to you, whether you’re selling IT equipment, software, or any kind of services? The piece of software that does kind of magic against all form of rationale, the guy with10 years of experience in a brand new technology, no kidding, happened to me few times.
The next question is what to do when the customer goes wrong.
I would recommend that you avoid, at all cost, pretending that you can make it.
This might help closing a deal shortly, and will fire back once the customer realizes his pain few months and few millions later.
As a professional sales person, you may rather want to opt for the following, probably in this order: Try to educate your customer.
Not the easiest one, it requires a level of confidence that is not always available; if you’re fortunate enough to get a customer who is willing to listen to you and understands why his request was a non-sense, don’t forget that he won’t feel comfortable getting back to his board to tell them about his mistake.
You may need to help him in redesigning the request.
Deny the request and tell your customer why you deny.
This might hurt you on the short term (missed sales opportunity) but it won’t take long before it builds a great level of confidence that pays off on mid-term and long-term.
Yes, the customer is king.
And ancient kings enjoyed being supported by fools who had the power to tell them when they did something wrong.

the customer is king