Not the perfect solution but I would prefer one like Wikipedia & others use. Allow flagging by users if a news story lacks citations or credible references. Uphold all journalism to a higher standard. For the most popular stories on Facebook have a trained employee from Facebook research it or crowd base it with users you trust. Show users a message that says whether the news article has been marked as false, questionable or verified. Facebook could even charge money for instant review & verification to news outlets. As machine learning gets better & has more use cases to look at, they could possibly offload the work from humans as well.