Easier algorithm: organizations with a long record and reputations to uphold, and which issue retractions when their stories are found to be factually incorrect, are real news. (Even if they are imperfect and politically skewed.)
Sources should be critically evaluated constantly, but sources that are usually more off should be treated differently than sources that are usually more on.
But that's the point. There seems to be a large number of people and organizations (including the US President) who are NEVER interested in issuing retractions or admitting fault - when something is pointed out as factually false, they just repeat the falsehood louder even when there is stuff like audio or video evidence that directly refutes it.