A friend of mine launched their book via Booksprout which allowed the book to be sent round as a preview version to a select number of reviewers. This is then timed so that on release day, all those people leave a review of the title on the Amazon page, and if those reviews are mostly positive, then it helps the book shoot up the rankings and secures much higher sales. This method has been used to create "Bestsellers" which basically means they sat at the top of a particular Amazon book category (of which there are many) for a set period of time.

You'll see a lot of new writers marketing their books as the "Bestselling guide to X" but I'm not to sure if the "Bestseller" status is really valid as the system has been gamed in a lot of cases.

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