As I have checked, I would like to inform you that in cases when the order is shipped and after that buyers wants to cancel the order then as per the amazon policy seller can deny paying for return shipping charges and then the buyer will have to pay the shipping charges.
Good to hear that :)
I am happy too as our sellers are happy :)
Further, I would like to suggest you that please contact the buyer and request him to initiate the return request from his end and thereafter you can authorize that request.