This will double the current amount of the item traded. 1.Save your game first. 2.Trade the item you want to another player. The other player could trade you 0 item. 3.Exit to the main menu, when asked if you would like to save, just select "No". Reload your game. 4.When you load, you would still have the traded item and also the other player. 5.Have the other player save his game then have the item traded back to you. Save your game. 6.Have the other player follow step 3. Now both of you have the duplicated item. 7.Just follow the steps above until you reached the number of items desired.