There might be necessary to correct product price in once placed order. It may occur for some reasons: cost may be altered on Taobao itself from the moment of placing order to payment or due to currency rates fluctuation.
You can alter product price on order information page in admin area by pressing "Change Price" button. As soon as you set the new product price you will see updates:
Important! After altering price in admin area, the user whose order was subjected to change should confirm the new price and pay/get the rest of the amount.