The picture is not big enough or good enough quality to say anything definitive, to me at least.
Now the underlying stamp of a genuine, the Red Revenue, is engraved. Fakes would be lithographed. A fake Small Dollar would not be made from the unoverprinted/basic stamp, of which only a few are known. There are no known used copies (to remove cancels from), so it is suspected that the Red Revenue was never issued and probably destroyed at some point after printing the postal overprints. Go look in your Cinderella and junk boxes if you don't believe me.
How must this be a fake? It may or may not be one. The paper looks genuine, the print from what I can tell directly going to eBay
, looks right. It would be a strange and fruitless effort to try to fake a corner margin copy and then stain or stick an adherence in the margin. The only problem is the gum on this issue, often pretty badly disturbed or heavily hinged, ranging to so little gum there it hardly matters to call it even part OG. $3000 would be a righteous bid for a no gum stamp here. It could actually be NH or no gum, I can't tell for sure, but it has the look of a regummed stamp from the front with some gum soaking apparently showing through. Therefore it's at a no gum price if no faults are hidden. The seller only says "mint VF".
Bad presentation in a pocket didn't help this. I can't magnify the image, either.
Low prices can always happen for a variety of reasons. If it is stolen, would the seller care what it brings?
If the seller's earlier failures were fakes of better stamps, I could understand but not sympathize. A lot of dealers and collectors don't know, especially when they've never examined a proven genuine one before. The fakes of that expensive 1980 Year of the Monkey stamp fool a lot of people including dealers and collectors who really should know better. If you know that the black is engraved/raised on the genuine, that's the key, where the fakes are all litho/not raised. Heck, there's even an eBay
post about how to detect the fakes. Even Scott says "engraved and photogravure".