Answer: You are paying for a book listing on our website.
All promotion, whether that be via email, other websites and/or on any social platform is complimentary and designed to drive traffic from those avenues to the book listings on our website.
Even though your book may be listed on your own website, on several buy sites and some review sites, there is still much value in having your book listed on yet another site.
The more mentions of your book across the web, the more popular your book appears to the search engine indexers.
Every legitimate and unique instance of an author’s book on more and more websites pings search engine indexers and each of those legitimate and unique listings helps push an author’s work higher and higher in the rankings. This is one of the reasons book blog tours are so popular.
A listing in the BookTweeter bookstore would be considered a legitimate and unique link for search engine indexers to crawl and rank. There really is power in numbers.