In Canada 5,000 copies a week make it a best seller although less could be considered to be a best seller. A book becomes a best seller because of someone determining that it should be so. It depends on publicity, publisher and marketing. There are best sellers in fiction and non-fiction categories. Often the best selling fictional book which some call trash continue with an increase in sales. It’s called mass marketing. (Harry Potter comes to mind) Driven by market sales and good publicity a mass-market book may not even be considered a literary work but because of tremendous advertising it has a cult following that does well on the retail side. The best seller list measures how fast a copy of a book is selling. If the book sells well but not fast enough it doesn't make it to a best seller list. A book may sell nearly a million copies yet never appear on any best seller list. The New York best seller list is the most widely known. By what formula do they gather info for a best seller list - no one knows. It has been suggested that a book, which does not appear on the NY best seller list it, isn’t a successful book. Sadly, some people actually believe this and look only for fiction and non-fiction books listed there. It’s about sales and marketing. The money racket often sees some great literary work go completely unnoticed.