What are the requirements for a book to reach a best sellers list?
There are no doubt different best-seller lists compiled by different organizations. The New York Times bestseller list reflects retail sales surveys of independent and chain bookstores, on-line mulitmedia websites such as Amazon, university bookstores, departments stores, discount department stores, and supermarkets. I believe that the figures are a sampling of each of these sources, not a complete count of all books sold.
In recent years, the categories of bestsellers have been expanded by the New York Times. For many years, there have been separate fiction and non-fiction lists, but now there are lists for trade fiction, those oversize paperbacks, mass-market fiction, those smaller paperbacks, paperback non-fiction, and self-help hardcover and paperback.
Sales is one portion of this equation. I think that a requirement for a book to become a best seller has to include the ability to generate "buzz" as a part of its presence on the list. In the online world, this might be appearance in blogs and creating enough attention online so that mainstream media forms are able to find attraction and similar attention. This would translate into sales and presence on the best sellers list. The more a book is reviewed would also assist in generating enough attention to place a book on the best- seller list. Finally, I think that most books which appear on the best sellers list have found a good combination of public relations marketing and the appeal to a particular niche which would be compelled enough to go out and purchase the book.