Several years ago, I had a good friend, a long time diamond dealer in Philly, who bought a 7ct E-VVS1 pear shape knowing it was HPHT enhanced. He paid next to nothing for it. Less than 20% of the 5 carat Rap sheet price. He was a taking a chance, but thought "How could it be worth less?" After owning it for more than 5 years he came around to the understanding that he could only retail the stone as there just was no dealer who liked it as much as he once did.
I believe he eventually sold it for just about what he paid to a consumer who felt that they wanted to pay next to nothing, or as little as possible, for a fantastically beautiful and well cut diamond. I found it very difficult to believe he was not able to sell it for a profit. There was nothing at all wrong with the diamond or the way it looked. It is all about some the inherent traditional conservatism of the diamond trade. Whether this is a justified conservatism or not, it is the way it has been for a decades. This is not a new treatment. Personally, I think there are beautiful and very inexpensive diamonds of this sort floating around worthy of consideration. Bought very inexpensively, they are not a bad deal. You don't want to overpay and to get to the right price, you must be well informed.