In this rather shocking video, Derek Muller of Veritasium exposes proof of the fraud behind Facebook Ads. Anyone can purchase fake likes from a site like BoostLikes, which uses click-farms in foreign countries, but the legitimate method of acquiring likes is supposed to be to use Facebook's in-house advertising service to promote posts and pages.
However, boosted posts and advertised pages using Facebook's official system appear to generate likes from Bangladesh, India, Egypt, Sri Lanka and the Phillipines, where users don't engage with the actual page at all (exactly the same results as when using these black hat companies cheating the system with fake user profiles and click farms).
To complicate matters further, having thousands of fake likes creates a large, unengaged user base, which detracts from the organic visibility of your posts. In other words, people who legitimately like your page are less likely to see your posts if you have a number of fans who don't interact with your content. As a result, you may have to pay to promote your content to get your actual target audience to see it, which makes the whole practice of Facebook Ads seems a little bit like like a pyramid scheme.
Facebook's main revenue model is based on advertising, but the current system of promoting posts and pages for likes seems like fraud.