An article called Are Book Trailers Effective? at what is now Build Book Buzz quoted a Wall Street Journal article on the subject. "There is scant evidence . . . that the average book trailer actually has much impact on book sales."
Hey, but that post and that article are both four years old. Everything's changed since then, right? Besides, my book trailer will be above average. And that article wasn't about above average book trailers, now was it?