Well, you have two original and authentic Krag 1896 carbine rear sights here to compare. As Butlers has pointed out, if the fonts or positioning of any of the details of the sight are not exactly the same as the two authentic ones shown, you can consider it a fake. People will buy it but it should not be misrepresented as authentic.

I would never buy something I knew is a fake to put on one of my carbines to make it "correct". Other people might but few who use this sight regularly.

Good luck. Thanks for sharing. It's always a good lesson to look at the details closely. (Including me!)