Sorry -

No, you are not required to pay for return post, if the buyer goes thru dispute paypal will ask them to return to you at their cost.  However, as a seller I do pay return if it has been my error (typo in size etc) or even if the item is not exactly the right colour etc (I usually send a pre paid satchel and the buyer simply has to pop it in a post box) Having said that a seller is not uner any obligation to do so. If the postal cost is less than $10.00 I would usually pay return  as a customer service gesture. Really up to you though.