I would argue that Facebook ads are not really for selling products (at least in the case of authors and their books), but for building engagement and your brand profile/awareness. From there, you slowly nurture the relationships you create on the platform (e.g. by posting more content they might like—aka content marketing) and sales naturally come from that.
Edit: I should add, the content marketing approach is a slow burn. It can take time to get traction. But you can build a decent sized audience and elist from it over the course of a year or two.
80 percent failed... which means 20% worked (Which if true, means that if you get a grasp on it, your competition is low) which goes along with the Pareto Principle I talked about before. Many years ago I advertised online via FB among other platforms. A lot of my peers in the same business did not have success but most of that was down to they had no clue what they were doing or whom they were selling to.
Any advertisement in any business must be dialed in, tested and retried. I think a lot of people think they can throw x amount of money at it and it should bring about great results within the first couple of tries.
Advertising brings about one ego ie 'My pizza is the best they will find me naturally or 'Word of mouth/Recommendations will sell my book' but the truth is you have to advertise.
One last thing and this in my opinion shows the author of the FB ads don't work article is clueless....
"How do you make money advertising a free product?
Answer: You don’t. "
I'm not going to go into a long ramble about this though I am tempted but I will say this. People think that immediate sales is the key metric in advertising. They can be depending on your goal. But that is the problem, most people advertising havent a clue of what their goal is.
What if you advertised a free book to 1 thousand people for 100 euros ? According to the article you lost money. What if 100 of those people bought another book from you at 3.99 ? And out of those 100 people 15 became life long fans buying everything you print?
Simple answers to complex ideas never serves anyone.