Let me clarify a couple of things. I never revealed who I purchased this item from, and never discussed it with anyone on this forum. If I felt that the seller had intentionally mislead me, then I would have had no issue doing so to protect other members.
However, I believe that the seller acted in good faith. I think that he did not realize the stone was not authentic, and was mislead as well by the original seller. I, of course, have no way of proving this. But what I can prove is that the stone I received is not a thuringian.
Secondly, the seller has agreed to allow the stone to be returned. Furthering my belief that he does not believe that he sold anything other than a genuine Escher.
Lastly, I also purchased a coticule from this same seller in the same transaction. I am extremely happy with this stone and am glad to have it. I know that there remain great stones in his collection for sale.

I did not intend for this thread to be an indictment on anyone's honesty or character. I merely wanted to ask more experienced members how common it was for people to sell fake stones (intentionally or otherwise). The result to the consumer is the same.