http://www.businessinsider.com/facebook-admits-to-miscalculating-web-share-live-video-metrics-for-advertisers-2016-12
Additionally, they have a very weird take on geography. Target a country and you seem to be rarely targeting people in that country. Default setting is to include people "with an interest in" that country, which is nuts. Even when we set to "lives in" 40% of the people we reach are clearly based elsewhere.