As you may all know, Blizzard offers a service where they can reverse a recent server transfer that wasn't agreed to by the original owner of the account. During this process, your character loses all the gold/items he had made on the new server and his gear and currency gets reverted to what it was when he's back on the old one.
Now I know some people are going to be confused about this so here it is in simple math.
You on the old server with 200g
*xfer server*
You on the new server, somehow gain 300g + you now have 500g
*email blizzard and get the revert service*You on your original server with your old 200g
Using this trick you can do a simple gold dupe. Let's say you have a friend on another server who needs money, xfer to his server, trade him all of your money, get the revert service, and your back on your old server with the gold you used to have and your money payed back onto your credit card.
-Don't use the credit card you use for WoW time for the xfer-