Considering that the book, published by WorldNetDaily, came out after President Obama released his long-form birth certificate, it's fairly remarkable that the title made the bestseller list at all.
The book, it's worth noting, received an early boost from Matt Drudge. But there's another catch here: the Times placed a dagger (†) symbol next to the entry for "Where's the Birth Certificate?" on the bestseller list, indicating that "that some retailers report receiving bulk orders."
This is not unusual in the world of conservative publishing. Mitt Romney's campaign biography debuted on top of the NYT bestseller list last year, but it was later reported that Romney was asking institutions hosting his speeches to buy thousands of copies of the book at a sharply discounted price. It's to the advantage of publishers to sell books in bulk, thus landing on the bestseller lists and creating buzz.
So it's pretty much impossible to know how many individual conservatives are buying Corsi's book in good faith and with a genuine commitment to birtherism.