https://www.brentozar.com/archive/2010/01/the-economics-of-w...
I made more money from Amazon affiliate fees linking to our book than I did the actual book. Way more. If you’re out to make money short term, you’re better off writing book reviews then books.
Having said that, the book gave me some credibility with clients for a couple of years when I was starting a consulting practice. When clients asked, “have you got experience with performance tuning databases?” I was able to point to the book. Today, with self published books being so prevalent, I don’t think having a listing in Amazon is as influential as it was.