Below is my assessment of PAID CLICK-THRU ADS for my two (non-fiction) books thus far:
1) GOOGLE ADWORDS: Thumbs Down (expensive per click, results were a little more website traffic, but very few book sales)
2) FACEBOOK ADS*: Thumbs Down (expensive per click, results in a little more interaction with FB Author Page, but very few book sales) *NOTE: The above is based on the standard FB ads. I might try the FB Power Editor tool in the near future to see if I get better results by narrowing the target audience.
3) GOODREADS ADS**: Thumbs way down (expensive per click, and very few readers actually clicked on my ads despite trying many different versions of the ad) **NOTE: Goodreads Book Give-aways: Mixed Bag (using 3 different give-aways, the 16 paperback books I distributed only netted 4 book reviews, but some of those reviews were harsher than Amazon reviews).
4) AMAZON SPONSORED ADS***: Thumbs way up! I've tried several different Amazon ads for my first book since November and almost every one resulted in more profit from book sales than the cost of the ad. My price per click is usually around 25 to 30 cents. Very impressed with these ads and will continue to use them for my first book. ***NOTE: These ads for my 2nd book (a self-publishing guide) have NOT been fruitful, and I'm not sure why. In the past 2 months, I have tried 3 different ads for my 2nd book and none paid for themselves. I may try once more, but will likely "cut bait" if that is unsuccessful.
How does my assessment compare to your experience with these ads? Please let me know what you think.