User Activity

I received a faulty item about 2 weeks ago (item was used but had stains on it which weren't indicated in ad). I got in touch with the seller who was understanding and agreed I should return the item & would then receive a refund. I promptly returned...
The box I needed to use on account of the size was bigger than I anticipated so the postage was around $35 more. What's the protocol on asking for the additional postage?