I might be treading on thin ice here, but more cultural diversity at ABC could have prevented this. The Knob Creek machine gun shoot is kind of famous in gun-enthusiast circles. With the number of machine guns being shot and the number of hollywood style gasoline explosions going off, I do think I would have recognized the source of this video if it were presented to me without context. There are many videos of this event from different years and from different spectators, but they all generally look about the same; tons of tracers and tons of gasoline fireballs.

I am not a combat veteran so the following is speculative, but I suspect the footage may look suspect to combat veterans as well. Big orange fireballs like that are from milk jugs of gasoline, not high explosives. That sort of thing is done for visual effect, not lethal effect. Certainly vehicle fuel will catch fire on battlefields, but I can't help but suspect the video would look "off" to a combat veteran.

You can start by asking the source who they are, who they work for, how they came to be in Syria, etc. Then try to confirm that information independently. That's what journalists are supposedly trained to do. If the source can't be corroborated, don't use the video. (Just like a journalist wouldn't attribute a quote to someone if it couldn't be verified.) Any reputable news organization would have a fact-checking department that does this kind of stuff.