From the site:
Can you judge an ebook by its cover? We all know that what’s inside a book is what counts. But with the explosion of ebooks — especially free ebooks — how can you tell if a book is worth downloading?
Every day, several hundred free Kindle books appear on Amazon. We don’t mean to be negative, but 99% of these books are horrible. They are either scammy books thrown up quickly to make a quick buck, or they are sadly amateurish. Either way, you probably don’t want to waste your time downloading them.
At ShelfBuzz we believe that a professional, well-designed cover usually indicates that the author cares enough about his or her book to invest in it. So the book might be worth checking out. That’s why we evaluate more than 200 free Kindle ebooks every day, and pick out the few that have professionally-designed covers.