Facebook has taken serious proactive approaches to combat click fraud. There are two kinds of clicks that Facebook identifies as invalid:
Clicks from people that don’t "indicate a genuine interest in the ad or show signs of ad testing." Such as repetitive or accidental clicks and visits.
Clicks generated through means prohibited by Facebook's terms of service, like fake accounts, bots, scrapers, and  browser add-ons.
Facebook will not charge advertisers for clicks that are determined to be invalid, and has some automated means of click fraud prevention, though they have not been made public, but for the most part, the social media giant puts the onus on individual advertisers to discover and call out click fraud. Once click fraud has been reported, Facebook will conduct a manual review of the traffic in question and take appropriate actions.