Here is an example of why it is important to pay attention to an advertisement's provider: I stared at this ad for quite some time and wondered what Facebook's Social Top Ups product was. Turns out it is NOT a new Facebook promotion to drive Credits, international usage, etc. Turns out it IS a developer's product (Social TopUps) and their ad unit is made to look like a Facebook product (not sure this is / should be allowed). If you dig in, the ad creative is similar to Facebook's mark(s) but at much lower quality... and the app's landing page describes the product:
"Roamware's Social TopUps Service allows a Facebook user to directly recharge a mobile subscriber's prepaid mobile phone in another country, as long as their mobile network operator is a participating carrier in this Service."
I suspect the ad unit converted terrifically from impression to click. And it probably lead to higher-than-average install rates... but the unit is sneaky and yet another example of why it is important to pay attention to the source of ads (on Google, Facebook, etc).