Woah, there is a cod system in place? All this time I had no idea. When I was trying to sell a cyan crystal the other day some asked about cod, I thought they were kidding. Off to do some research I guess. Learn something new everyday, thanks.
Indeed I sold 2 Cyan-Blue Crystals the other day to a guy for 450k he didn't get the crystals I mailed him until he sent me back the price I entered. The system works perfectly if they don't pay the price you will get the items back in the mail.