When some authors come to me for book-marketing help, the often begin by telling me, “There is no other book like mine.” In many cases they are not aware that competitive titles exist. I suggest a search Amazon or the other online stores using their topic as the search argument. Google your topic to see what else is out there. If no other titles exist, perhaps there is no demand for your content. If you wrote The History of the Ballpoint Pen Sharpener, you would probably not find any existing titles since there is not much demand for your content.