This March, a book that advances an outlandish conspiracy theory—a theory whose name I will not mention—soared in Amazon's sales rankings. The book's rise was helped greatly when the ecommerce giant put the book on its carousel of recommended titles, which is shown to shoppers who aren't searching for that particular book. That fueled more curiosity and sales. Which led to more recommendations.Learn more about your ad choices. Visit megaphone.fm/adchoices