[angersock]

Might as well point out the paragraph buried in the article:

> And that’s the thing: By and large people aren’t selling guns illegally on Facebook. This isn’t a black market. The gun sales orchestrated on Facebook appear to be aboveboard in the eyes of the law; they’re just happening in violation of Facebook policy.

tl,dr; reporter uses communication platform to conduct run-of-the-mill personal firearm sale.