Shipping costs are very wrong due to agent

Problem 1: I have 8 orders that the agent asked me to pay extra for shipping because he miscalculated the cost and was returned. Is this normal at CJ? I am not satisfied with this, the extra charge is as high as or more than the previous shipping fee.

Problem 2: I have repeatedly encountered products on sale with constant price increases but have not received any notification from CJ regarding that issue. Mostly due to the wrong calculation of shipping costs by the agent.