Involves 3 players.
1) Player A select Player B and type /trade .
2) Player B press OK to open the trade window. Keep it open.
3) Player A trades and press OK.
4) Player A type /trade . Player A window will close but not Player B window.
5) Player A select Player C and type /trade .
6) Player C press OK to open the trade window. Keep it open.
7) Player C shows the item in trade window thats going to be duped.

Player A trades and press OK.
9) Player B trades and press OK.
10) Player C cancel the trade.
11) Player A should now have a copy of Player C items.