Amazon is expected to be good sports and take the loss exactly because that is their business strategy. Their mission statement is something like, "we seek to become Earth's most customer centric company." If they didn't have a relaxed refund policy, they wouldn't have the reputation they currently enjoy.

Contrary to what you've said, they do have public trust: just in the form of "Amazon does right by the customer." It's trust, not morality, that forms these expectations.

For the trustworthy customers who are equally concerned about their reputation, they wouldn't dare "cheat the system" by exploiting a pricing glitch. For them, there is symmetry of expectations.

The asymmetry only happens for customers who do not care about their reputation for being trustworthy. This can go the other way as well: an unscrupulous company who takes advantage of naive and trusting customers.