It would appear that duping exists in Diablo 3. Thanks to the game’s newly implemented profile system, which allows players to view what others have equipped, one potentially duped item have surfaced.
The item, called Arcanum Mind—an offhand weapon for the Wizard—bears a lot of powerful stats and appears to be equipped by numerous players.
It seems like evidence of duping as the item is identical in each case, and goes against Diablo 3’s random item generator. It’s a statistical impossibility that the system produced identical rare items, all of which share the same name.
Assuming that it’s an actual case of duping, Blizzard will have no choice but to investigate the issue and ban those involved, or at least reimburse players who may have inadvertently purchased the item through the real money auction house without knowing it was duped.
It’s necessary for the company to protect the integrity of the game’s item system as transactions between players involve actual money.