This all adds up to numbers that are ubiquitous, closely watched — and of dubious value. The targeted marketing campaigns contribute volatility to sales-ranking numbers that are inherently unstable. Outside the top 1% or so of books, few sell multiple copies a day, so little separates books with rankings tens of thousands, or even hundreds of thousands, apart. Morris Rosenthal, an author and publisher based in Springfield, Mass., who has studied the Amazon charts, says a day without a sale can send a book ranked 10,000 to as low as 50,000.
It sounds just like any other ranking system. If you have a few dollars to spare, you can rise to the top easily.
Source: Wall Street Journal