At various times, books, e-books, and kindle fires.
Amazon actually shifted the pricing on books and e-books by selling them at below what they were buying them at for prolonged periods of times, and drove rival book sellers out of business by doing so... and then didn't raise their prices.
Do we know if they still sell books at a loss? I'm guessing with their volume and many competitors killed off they have an insane control over their own buying cost and can force that price to now be profitable, but it'd be interesting to know either way.
Well, from their earnings reports, their gross revenue has grown dramatically but their profit margin remains near zero because they spend every additional dollar they make on growing the company.
Amazon actually shifted the pricing on books and e-books by selling them at below what they were buying them at for prolonged periods of times, and drove rival book sellers out of business by doing so... and then didn't raise their prices.