Relative to eBay's policy, you must return the item with a shipper that has tracking the item as a absolute return method.
I just was screwed by a purchase from China, where the items cost $99, were incorrect, the seller agreed they were incorrect. The cost to return with tracking was $100, so to foolishly save the seller money, I shipped at lowest cost of $26. EBay canceled the "case", as I did not return per their rules. The seller still has not received the returned items, and I doubt if they ever will be honest and refund any money.
Lesson learned, don't buy from any place outside your continent, and any returns to be sent back, no matter what the cost for tracking. It just seemed irrational to spend more money to return then the original item.