Earlier quoted context omitted.
In my ethical framework it is more than fine to take advantage of a mistake by one of the largest companies in the world. They'll take advantage of you if given the chance.
At what size company would your ethics require you to reverse course and treat them the way you would like to be treated if you had made the mistake?
If the company is Amazon-sized you are taking profits away from Amazon shareholders due to a mistake in the algorithms that drive Amazon's profits, which is nothing if not fair.