Yup, it's pretty easy to manufacture a "best selling" whatever book --- a mere 50,000 sales will usually land one on the various lists. Harry Potter recently skewed that by making reading fun again, but I remember Pat Buchanan got various of his books to "best seller" status merely by giving them away during political fundraisers as thank-yous for donations. Calling it a "sale" was just his standard political BS, but a lot of pol-books pull the same stunt.