I am always wary of final judgments about authenticity of things described from afar or seen in photos, and I try to limit my input to the probability, leaving it to the real experts to judge material, stitching, etc. Army signal flags of the standard Myer design (contrasting color square on plain background of a different color, e.g., red on white, white on red -- not the star flags, about which, from smaller numbers, we stand a better chance of verifying awardee) mushroomed on Ebay around the turn of the century. Most were small, with two-piece pole or metal, some with web or cloth cases. One ID'd as "Confederate" caught my eye and was already in five figures. I inquired of the seller, casting doubt on the ID. She said that "they came from an estate sale in Georgia -- what else could they be"[!]. I explained that they were probably WW I vintage and convinced her -- in unusual courtesy, she took down the offer, notified the top two bidders that question had been raised, and that, if it turned out the flag was Confederate, they'd be given first offer.
Never heard anything further, but it restored (albeit temporarily) my faith in human beings.