One of the elements is that "the effect of such discrimination may be substantially to lessen competition or tend to create a monopoly in any line of commerce". I don't think Amazon's dynamic pricing satisfies that element.
That's up to government commissions to decide whether Amazon "tends to create a monopoly" with dynamic pricing. Amazon discloses nothing about its technologies to the public. What we see is, (1) Different prices for different users; (2) The conflict of interest with the merchants Amazon.com hosts, as Amazon serves both as a host and a reseller; (3) Amazon has an access to other merchants' traffic and prices, and is able to diminish their chances to compete with the service.
