To perform a partial credit card refund in PetExec: (the steps are the same as for a full refund, you just change the amount of selected service in the refund order)
Begin in the pet owners purchase history. From the owner menu-->purchase history.
Click on the order ID for the order you want to refund. To refund back to a credit card, you must have an existing order with a credit card transaction.
From the next page, click the Apply Refund button:
On the owner refund screen: