My buyer pay me the full shipping fee for her second scarf (she is supposed to get shipping discount), so I get the chance to learn how to refund money from paypal.
1. Send message to buyer to let her don't worry about it .
2. Check "Recent Activity" in paypal, find the record with extra-payment.
3. Click the "Details" of the payment record to open "Transaction Details" page.
4. Click "Refund Payment" in the end of "Transaction Details" page.
5. Filling the amount you want to refund(the default is fully refund)
6. Confirm your refund.
7. There will be a record of refund added in "Recent Activity" list.
After that, the extra-money are refunded and the Transaction Fee of the extra-money are back.
Wish you good luck in Ebay & Paypal.