How to determine critical customer requirements

For any business, customers is the final authority that determine the final value of any product or services with their decisions to buy or not. This decision are based on complex system of critical customer requirements. 
If you know how to decode those critical customer requirements you can make decision on business process with so much confidence.
Say, as an example, I am planing to fly from Austin to Chicago with 2 bags. I will search for airline with criteria as low price and one that allow 2 bags. After searching, i figure out Southwest Airlines allow me to carry 2 bags at fair price which is close to nearby airlines. I decide that i will fly with Southwest airlines and buy the ticket. So of all the airlines, Southwest is winner !
Why Southwest in above example because of customer value. At same price i am getting more value. You can describe customer value in four areas: Cost, Quality, Features and Availability (CQFA).
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To prosper, a business process must do very well in at least one of those four area. Southwest win over feature as 2 Bag while prices are still same.
If a business can be best in class in one of those quadrants, they can thrive. But always, remember, level of the bar in each quadrant is rapidly changing, so always determine what is critical to your customer on continuous basis.
I mean this technique is simple but u now, know what add value to customer. It’s CQFA.