Exactly. The easiest way they found to prove it's a cultured diamaond is that it's TOO perfect.

there are some other light refraction tests that they can do... but they are only about 60% accurate. Put a perfect real diamond next to a cultures diamond and it's almost impossible to tell them appart. Usually the only way to tell them appart is to use very high magnification with UV/IR light and a spectometer and find the one with the imperfections. Keep magnifying till you see something imperfect. Once you see something that's imperfect, you've found the real diamond.