how can a seller lower or delete change shipping cost after item purchased

[krill7]

I want to combine ship for a customer but am unable to change shipping cost on the invoice ?how can I provide this service to my customer?

[catsnewwife]

Has she already paid you? If so, I don't think you can change the invoice. In the past, I have just refunded my customers the overage they paid (but I still got dinged for the fees on the postage quoted).