First Time Poster long time reader. Don't know if this has been posted before.
Posting from the Horde point of view.
Make an alt and post the item you want to sell. Now make another alt and find a person you think might have enough gold for the item you want to sell make it is the lowest price. Tell him you are on the other faction and don't have the money on the Horde side and you will pay him an extra 5g or something for the auction house cut so he will buy it and put it in the neutral auction house. If he says he will wait till he buys the item then when he buys it then immediatly delete the character. Get the money from your alt that sold the item so you can send it to your main and delete the alt also. At in the end he will be in Tanaris or whereever waiting for somone to buy it from the auction house.