I had an email recently from someone who got an offer to buy a program that would help make him an Amazon best-selling author.
I know how those work: you get a number of online marketers to promote your book to their lists, asking everybody to buy the book on a certain day (sometimes even at a certain hour on that day). The book buyer's reward is a whole bunch of bonuses provided by the marketers, usually in downloadable form. In return, the author either agrees to do the same with his or her list (if they have one) next time, or they pay a commission on the sales of the book, or they pay a flat fee.
This was a hot topic about a year ago. It has cooled down since but these offers are still flying around. My correspondent wanted to know whether it was something worth spending money on.
My opinion: No.
First, you have to look at what is being guaranteed. Usually it's that you will be number one in your category on that day, or even just part of that day. Not number one in "books" of course, but maybe number one in "bird watching" or "classic car restoration" or whatever category your book fits into. It applies to non-fiction only, by the way.
Let's assume you achieve that. So what?
Yes, it gives you the right to say, "My book was an Amazon best-seller!" But people in the book trade know that doesn't mean anything unless it is sustained. They can go to your book's listing and they'll see that currently it's 134,656 (or whatever) and they'll know that the best-seller status was, shall we say, limited.
Furthermore, how would you feel about saying your book was a best-seller when you know it was only a technicality? Some people would feel just fine, but a lot of us would feel that even thought it's true technically, it's a claim that lacks integrity.
There are better ways of spending your money, including sending review copies to influential bloggers in your field and taking out small classified ads in relevant trade publications and small ads on websites.
(For more on marketing your book, including guerrilla marketing techniques, see my book, "Your Writing Coach," available from Amazon--by the way, it's genuinely number one in "authorship" most of the time--and other online and offline booksellers.)