Most evidence points to that being a misconception.
Here is how textbook prices are calculated, and why. New textbooks used to come with publishers' recommended prices printed on them, according to Neumann, but most publishers have abandoned that practice. Now, publishers generally charge bookstores 80 percent of suggested retail price, plus the bookstores pick up the cost of shipping. The bookstore sells texts at the publisher's recommended retail price. That leaves less than 20 percent gross markup in the textbook.