People trying to make a quick buck I guess. I wouldn't trust him if he told you it was a pure black diamond as you can see it came from Aquascape as a hybrid. Still a nice ray but not a pure black diamond. If you like it buy it and offer him $1200 LOL.
The seller should have done his homework more as it didn't take much evidence to disprove his claim.
Most people in the ray game can remember where rays came from especially the nice ones and I knew once you posted the picture that it came from aquascape, which came from center for stingray biology.
Here is the same ray when it was in possession of center for stingray biology. Toggle down to the 5th ray.
http://www.arowanaclub.ca/forums/showpost.php?p=47115&postcount=2