Who turned him in? There's no way the ATF just happened across some random person on Facebook who just happened to be selling firearms. I'm assuming there's a Facebook algorithm that tracks specific words and flags someone's profile for review, and then forwarded to the ATF, but I also am not discounting pine of this guy's "friends" reporting him to Facebook, who then, again, flagged the account and sent his info to the ATF. "When asked if Facebook tips off the agency about gun posts, the ATF spokesman declined to comment," should say enough