You have every right to whinge and should stand your ground and insist on the return postage being refunded.
I was put off eBay by the ridiculous postage charges that the sellers are allowed to charge and rarely buy anything and then only if the postage is reasonable.
Have been selling from an eBay shop for a few years now and do not charge at all for postage. Also have a Freepost address so that if anything has to be returned (sometimes for a change of size) it does not cost the customer anything. Have had this policy for nearly 20years in my mail-order business and do not intend to change. I firmly believe that if I advertise goods at a certain price, then that should be the price to the customers door. After all I am mail-order only so it is not as if there is anything `extra` about delivery.
eBay, from time to time, do make half-hearted attempts to try and control the situation and do now give some benefit to those of us who do not charge but I really think it is up to the buyers to ignore goods with stupid postage costs.