Seller wrote to ask for more shipping than the buy it now listing

[zno2]

Hello!  Bought and paid for $20 tablet case item via paypal and buy it now .  Item included 5.49 shipping which was paid within buy it now. Seller messaged today that they had to pay $9 additional at post office and sent receipt as proof.  So did I obligate to also pay the additional $9 for shipping?  I would not have bought the $20 item if I knew I would be paying $14 (70%) to ship. Thank you have a great day.