We are sorry for the delay in our response, please excuse our late reply.
We would like to inform you that your buyer has to pay only the sum fixed within the order (product and shipping fee). He has not to pay any additional fee as the price on A is a fix (final) price.
If there is some custom duty to pay, this is the responsibility of you as a seller.
We hope that we were able to sufficiently assist you with this matter. For all further questions, please recontact us via the following link:
「買い手」を「売り手」に修正してください。すいません。