No just as everyone has suggested as long as the trade is not assigned on the later end and transaction not been completed, you can easily oress the back button and close the order, but once the order has been assigned to a particular buyer which means he is already on the move to make payment or has already done that, then you can't go back than to confirm the reception and same way if you're the buyer, your topic talks more about bitcoin trades and i will suggest you move the thread to trading discussion.