> man-made diamonds are much more likely to be purer and flawless.

Hmm, both natural and man-made stones have price/quality trade-offs. I am no expert in the field, but I think both kinds are post-sorted into quality grades based on what flaws are found. And I guess labs can also tune their growth parameters for different trade-offs.

So yes, for a given price and size, the artificial stone will have better quality -- but that is just another way of saying they are cheaper.