It’s amazing what can happen when two Amazon.com vendors enter into what is effectively an automatic price raising war with each other. The short version: one vendor was automatically setting the sales price of a book that he was offering to be 99.8% of a second vendor’s price… and the second vendor was automatically setting his sales price to be 127% of the first vendor’s price*. The number got up to almost 24 million before anybody noticed.
Interesting thing, the used book retail industry. Especially when you mix it with the Internet.
PS: This is the book:
*The guess by the author of the linked post is that the second vendor didn’t actually have the book, but could get their hands on it if somebody actually ordered it; and as having a good feedback record is a plus in this business, somebody might actually order from them even if they’re selling it at a higher price.