I'm pretty sure the Gold dupe hack for World of Warcraft doesn't exist either. Anyone offering to send you the gold dupe hack is actually sending you a keylogger.
A keylogger is basically a trojan or virus that captures the information your keying and transmits it to someone else. This is how World of Warcraft scammers steal accounts and gold from WoW Players.
The easiest players to dupe and steal from are greedy ones. So when you think about it, the Gold dupe hack is perfectly named -- because the Dupe is the player who downloads one.
Be careful to avoid downloading any so-called "gold dupe hacks" on torrent networks. I can just about guarantee that you'll be downloading a virus of some kind.
There are easier ways of getting more gold into your account. There are several different WoW gold guides available that explain all the shortcuts and the best strategies to use to get gold faster and none of them involved cheating, hacks or bots of any kind.
My preferred guide is Derek's Gold Guide, so I would take a look at that one if you are looking to amass gold in your account. It's a lot cheaper than having your account stolen!