When considering getting a Moissanite ring, I spent a significant amount of time researching the differences between diamonds and Moissanite, but I couldn’t explain or recognize the difference between doubly-refractive and singly refractive gems. We’ve even had jewelers who have looked at my wife’s ring and thought it was diamond. Admittedly that was a casual look and not a thorough appraisal, nevertheless, I doubt even a tiny percentage of the population could spot the difference.

Oh, looking at one or the other, almost certainly not. I mean that if you lined up 2 diamonds and a moissanite, I'd bet the average person would be able to pick out the odd one out.

Lie to them and say there's one diamond and they'd still pick the moissanite. Just being able to differentiate relatively with a biased test doesn't mean you can tell the difference one way or the other in absolute terms.