Even Amazon’s detractors readily admit that it is one of the most powerful tools for selling books since the Gutenberg press. But how that power is used is increasingly being questioned in a way it was not during the company’s rise.

Take, for instance, the different treatment Amazon has given two new Hachette books on political themes.

“Sons of Wichita” by Daniel Schulman, a writer for Mother Jones magazine, came out in May. Amazon initially discounted the book, a well-received biography of the conservative Koch brothers, by 10 percent, according to a price-tracking service. Now it does not discount it at all. It takes as long as three weeks to ship.

“The Way Forward: Renewing the American Idea” by Representative Paul Ryan has no such constraints, an unusual position these days for a new Hachette book.

Amazon refused to take advance orders for “The Way Forward,” as it does with all new Hachette titles. But once the book was on sale, it was consistently discounted by about 25 percent. There is no shipping delay. Not surprisingly, it has a much higher sales ranking on Amazon than “Sons of Wichita.”

So Amazon can essentially pick winners. Yikes.