People perceive things as valuable if they pay for them. This is a fact we have discussed on this blog previously.
Amazon is reporting that people will purchase more from a web site if they pay a fee to shop on it. You read that correctly. They pay to shop there and that increases the likelihood that they will return.
There is an implied perception of value in things that are expensive. Paying a fee to buy goods or services is more evidence that this tactic can influence perception.