Transferring gold and items from Alliance to Horde or Horde to Alliance is possible. The benefits are making more gold, playing tricks on the auction house.
This kind of business is not encouraged by Blizzard as if something goes wrong (many things can go wrong), they will not be able to do much.
The benefits for trading gold and items? You have access for two auction houses, you can buy cheaper and sell more expensive. Is not difficult to make gold by this method and why not, it can be very fun.
Trading gold Alliance to Horde and Horde to Alliance
Just ask in trade (/2 trade) chat for gold exchange or ask a friend, guild member who has a character on the opposite faction.
The risk here is that you won’t receive the gold from the trade. Be sure that the person you are trading the gold is level 85, is not guildless. At least these are some risks that will be eliminated.
Transferring items from Alliance to Horde or Horde to Alliance. This can be done by using the Booty Bay auction house or the one from Gadgetzan. Buying from Horde let’s say. You need one character in Orgrimmar that will buy items, one character in Booty Bay that will receive the items by mail and post them into the Auction House.
As Alliance, you need a close friend or guild member that will go to Booty Bay and buy the items for you. It is not possible to buy items with your Alliance characters from your Horde characters.
Risks. The biggest risk is that someone else, other than your friend, will buy your items that you are trying to transfer.
That’s why, post the items with high prices, 10k gold for a companion pet for example. Give 10k gold to your friend so he can buy the item, then you will get both items and the 10k gold. If you post the auction for 1 or 10 gold, other players might buy the items and you will lose a lot of gold.
How to stop an auction in WoW?
It is not possible, once someone bought an item that you are selling using “buyout”, there is no way to cancel the auction. You can talk to the player who is buying your item and ask him nicely to return it back. You can also offer some gold in exchange. If he refuses, don’t worry, karma will do the job.