I take back everything I said a few months ago about how great the KDP select program is. Amazon has apparently opened up their ad system to everyone, not just KDP select members. So the result has been a flood of people running ads for their books which has resulted in ads only being shown a few hundred times per month. Before this happened my ads were being shown 150,000 times per month minimum.
Considering that roughly ten percent of the displayed ads are clicked and then less than one tenth of a percent of those clicks results in a sale, the ads never were that great for selling books. The value came in people seeing an ad and then going to the Kindle lending library and reading a book there. when someone does that the author gets paid for every page they read.
I’ve noticed a lot of authors on Amazon complaining that all their sales and page reads have stopped over the last few months. Amazon may have screwed up bad with this because from what I can tell most authors who stayed exclusively with them did so because they could make good money. Many of them are now dropping out of the KDP select program and using other eBook distributors, which will only result in Amazon loosing royalties from book sales.