FBX is an ad EXCHANGE where inventory gets sold to the highest bidder. If FB over-reports views by a factor of 2X to advertisers, the average CPM that advertisers are willing to pay will simply fall by 50%. Sure, there may be a short time period before bids equilibrate, but FB is liquid enough that this would happen extremely quickly.
The same principle applies to people up in arms concerning "click fraud" on Facebook and/or Google's ad networks. As an advertiser, you really should not CARE if there is click fraud. So long as it impacts all advertisers equally, we're all bidding for the same quality inventory.
It's useful to keep in mind that the vast majority of advertisers on any liquid ad network will not be successful. It's easy to rationalize that the reason you aren't able to make the channel work is that the network "rips off" its advertisers. In reality, there is no incentive for them to do so.