Every e-book sold on Amazon has its own Web page, detailing the book's price, cover art, title and author, description and reviews. In the "Product Details" section, the page lists the book's "Amazon Best Sellers Rank," a number that gives the book's relative position out of all the e-book on sale -- the smaller the number, the greater the quantity of books sold. For example, the entry may read, "Amazon Best Sellers Rank: #521 Paid in Kindle Store." This number changes constantly; when Amazon sells more copies of a title, it usually lifts the ranking, but because the ranking is relative, it depends on the sales of competing books as well.
Publishers can participate in Amazon's Kindle Direct Publishing Select program, in which they agree to sell exclusively through Amazon for three months in exchange for free promotional tools. For up to five days per quarter, the publisher can offer the book for free, letting potential readers take a chance on an unknown author. Amazon ranks its free books separately from its normal offerings; the Product Description for a free e-book may read, "Amazon Best Sellers Rank: #637 Free in Kindle Store." By giving a separate free ranking number, Amazon gives lesser-known works a chance to stand out if they do well during the giveaway promotion.
The Amazon website lets you browse e-book by genre and has the option to view them by release date, price or popularity. In addition, Amazon lists the top 100 most popular books for a genre and lets you see them in terms of paid and free titles. The popularity lists take sales ranking and average number of review stars into account, and the first page gets the most popular titles.
Good ranking and reviews lift an e-book's visibility, making it easier to find among the many titles on Amazon. Unfortunately, some authors have resorted to gaming the system through buying reviews, posting fake reviews and buying their own books to boost sales. This has become a problem for Amazon, and has prompted the company to remove some of the questionable reviews.