I've self-published a number of novels that got organic 4-5 stars and positive reviews on Amazon, and unfortunately in my tries Amazon ads for books had negative ROI. On the other hand, Facebook ads had a very positive affect on sales, until some bizarre incorrect algorithmic decisions by Facebook made it too much of a pain in the ass to deal with their ad manager and I gave up on it.<p>In any case, if you're really interested in advertising you should give Facebook a try. As long as they work, their algorithms somehow magically find people who will actually buy your book.