No longer works - guild banks are disabled
Kudos for zenimax, I gotta say... they work way faster than blizz
I hope everyone had fun with it till it lasted
1. Download Auto clicker 3.0 by Schocker (or other clicker) and set it to click every 1 millisecond
2. Go to the banker and open your guild bank tab
3. Deposit stack of items you want to dupe (preferably 50 items in stack, since you're not able to dupe full stacks)
4. Enable clicker and mouse over on your stack in guild tab to withdraw it
5. Repeat as many times as you want (disable clicker after withdrawing, you don't have to use it while depositing - only withdrawing)
And there we go, if you were lucy enough you now have full stack of 100 items
Notes:
-Sometimes it won't dupe it and at times your item might even be destroyed, but chances to dupe / not dupe are 50/50 and chances to destroy only at around 10%.
-Don't deposit + withdraw items too fast, as it'll often causing guild bank to lag, you won't be able to deposit, withdraw or split stacks etc and you'll have to relog.
I managed to make 1mln gold out of 2 Dreugh Wax I bought from some other player in 2h, only by vendoring them! (that's how fast you can dupe items :] )