Something scary happened yesterday when I used Amаzon:
I was looking to buy some cat litter and saw that the 20l version was 17.50 Euros. Then I saw that the smaller size (10l) would have been actually cheaper per kilogram, so I clicked on that. Suddenly the price of the 20l version got reduced to 15.30 Euro so that it now was the cheapest version.
I then checked who actually sold each version and the former cheaper 10l one was from a 3rd party seller. The 20l version that had its price suddenly reduced was sold directly by Amаzon. I clicked on all sellers and couldn't find the 17.50 Euro version, so it must have also been the one directly sold by Amаzon.
Which most likely means that Amаzon has a (real-time) algorithm in place that when there is a product that is offered cheaper by a 3rd party seller, it automatically adjusts itself to always be the cheapest option.
Personally I'm not complaining in this case. But if I was an Amаzon seller I'd think twice about selling a product that Amаzon themselves sells directly too.