You don't fake your stats, you tell something true that is impressive unless you look under the hood of how the number was formulated. That's how you can get away with it legally. There's a famous old book called "How to Lie with Statistics" (it's on Bill Gates' must read list) that explains some methods companies use.
I dislike how FB presents their data by default, but if you know where to look or how to set things up it is something you can mitigate (unless you need to get view data into your ad server for something using Custom Audiences which they don't allow).
It is admittedly less of an issue for performance advertisers than brand advertisers as the former can rely more heavily on conversion tracking to inform quality.
Does it matter? Their effectiveness is proven at this point.
When have they proven the effectiveness of their ads? From my understanding, in fact it is increasingly being discovered that much of their clicks and likes, etc are fake.