"Dynamic pricing" has been around since at least 2000. An article on Lifehacker from 2013 reports that back then Amazon experimented with the idea but decided to abstain from the practice after some negative press. In 2005 CNN reported on a study at the University of Pennsylvania that found that a large majority of adults believed (incorrectly) that policies like dynamic pricing were illegal. That report didn't contain any new examples of the practice, but an article in Slate, from 2010, gave a few examples beyond the classic Amazon story.

It's my guess that the vast majority of people who become aware of the fact that they're being charged differentially are being over-charged. I may be wrong, but it seems to me that even though all sorts of people buy online, people with expendable income are also people who have access to, or have an interest in, information about this issue. Because of that it stands to reason that if and when they realize that they're being over-charged they'll also want to know if there's anything then can do about it. The Lifehacker article suggests a few possibilities. Whether these are workable or not, or worth the effort, is an interesting question. It's relatively easy to find a poorer neighborhood around where you live and enter its zip code instead of your own when buying something. It may be a bit time consuming, but it can work. Mac users might keep a Windows computer (preferably with an outdated operating system) handy for purchases. That would probably save some money, but I suppose that anyone who can keep that old computer around the house probably doesn't need to save too much money anyway.