It's really really hard to determine the truth. If I were you, I would find a seller with CSBs then research that seller. If they're selling fake CSBs I'm sure someone would eventually figure it out and post about it. Also, like mentioned above, picture comparisons are very important. Real CSB sellers should know the "phase" of their nem (red phase, yellow phase, etc) so you can photo reference more accurately. Looking at it in person is always the best way to check, that way you know nothing is photoshopped to make it look more like a real CSB but if you have to buy online, ask for new photos (size reference against a white frag plug for example) to see the size and color of it. If the reference object doesn't look right (has a weird color, shape, etc) then you know they're photoshopping. I also reverse image search the pic they post, just to make sure they didn't just lift it off google and are trying to act like that's the nem they're selling. Good luck!