When I sell that book I tend to sell it in multiple copies because people are buying for their entire group. (trainingauthors.com)
Maybe people are buying it for the 4 % + dividend. (alephblog.com)
Nu - Doom, for example, was one of Steam's top 100 bestselling games in 2017, even though it released in May 2016 (and I doubt most people were buying it for the multiplayer). (pcgamer.com)