4.3.4 Item Ducplication

So basically a guy joined our guild on wow-freakz 4.3.4 server and he had over 1000 epic gems with him, he seems to have an unlimited supply of these gems, essences and whatnot. So the thing is i am pretty sure he duplicates items somehow. First question is, is it even possible? If yes, how?

It definitely is, it also is on Blizzard´s official realms like entchantment-materials and also mounts, etc. are/were able to dupe.
I don´t really know how it exactly works, had it 1 time when the server lagged hard (later dc included) but that was the one and only time.

Take a look at my Sig if you want to buy the Dupe ;)