I am not sure how useful Amazon’s Sales Rankings are at times, but they are certainly interesting to watch. Lately I am more concerned with where my books fall in the search listing when a customer is looking for a book in the topics I have authored books in.
The long tail of Amazon kicks in when a book moves up in the search listing. When one of my books makes it to the first page of listings for a given search, sales pick up a bit more. To the extent Sales Rankings play a role in this, I cannot say, but I will say as my average Sales Ranking for a book increases, it moves up a little further in the search results which equals a few more sales, which equals a little higher average Sales Ranking, etc.
I do use RankTracer’s service to estimate sales based on Amazon Sales Rankings for the one book I don’t have published with CreateSpace (CreateSpace provides hourly sales updates). How RankTracer does this I have no idea and Amazon certainly is not going to comment about the process. My guess is RankTracer has some pretty good mathematicians who spent a lot of time monitoring sales of a set of test titles and creating an algorithm capable of good estimates.
Self-publishing expert Morris Rosenthal has spent years doing exactly this and has produced a graph he both updates and publishes on his website. Lately Morris is beginning to think Kindle sales are having an impact on the accuracy of his sales estimates system based on Sales Rankings. Based on following his blog for some time my guess is he will eventually determine a method of determining accuracy of both paper and Kindle book sales.
The other reason I pay attention to sales rankings is to try to judge the impact of an on-line marketing strategy or the impact of my e-newsletter. Book marketing is key to selling books for a self-published author and as much as I have learned about the field of self-publishing, and in the process increasing my sales, I feel like book marketing is the football Lucy keeps moving when I try to kick it.
The more cynical side of my brain thinks Amazon just likes to mess with the minds of self-published authors and uses its Sales Rankings to do so.