Thanks to the people who made a guess at my challenge.
Obviously I posted in a slightly confrontational way directed at jebrady03 because of the silly claim (since clarified)
"but, I've been told repeatedly that when someone KNOWS what they're doing with flash, you can't really tell they used it. I've yet to see an example of that myself, but I've had my eyes open for it."
Not least because of the inability to prove it to yourself. If you can't tell they used it, well, then you can't tell! You might have viewed thousands of images that have it, so it was really a challenge to your deconstruction skills. By your answer, jebrady03, I would take longer honing those than making blanket statements
It was shot with one on camera flash bounced off the wall to picture left, camera in M mode, flash in ETTL (far and away the best camera/flash starting point and setup), no FEC and zero ambient (because of the green fluorescent bulbs). The wall it was bounced off was a tool hanging wall lined with brown pegboard. I used a small piece of black foam paper and rubber band to make a scrim to stop any light going directly onto the subject (which
I learnt from here).
All in it is very interesting to see the variety of answers and several of them could have been right, and some were. It just goes to show unless you are very experienced and you have confidence that not too much post process disguising, layering, or adjusting has gone on it can be incredibly difficult to identify even simple lighting setups, and I am not placing myself on a higher pedestal here. Were I asked the same question the extraneous shadow dcm pointed out would have thrown me, there shouldn't be a hard shadow there, it must have gotten a spurious bounce from a closer object.
Now I will have to find a daylight/flash combo to test jebrady and anybody else up for a challenge.