Jemel Smith offers his book on Facebook, targeted to contractors in the Atlanta area
When a targeted business owner wants to read the book, they click on the ad. And it takes them to the offer on his web page. He tracks web page visitors so that he might follow up with future FB post and emails etc.
FB ad responses start out at around $10 to $20 each, but after a few weeks the cost drops to the $3.00 and $4.00 range as FB learns who should see your ad. My experience has been that one of twenty book readers will become your client.