Hello, misssherlock59,
If you have received a full refund, the general view would be that you no longer own the item and should return it to the seller.
There are some exceptions to this, in my view. For instance, if what you purchased turned out to be a fake, destroying it is probably a suitable method of dealing with it. If it's damaged or not as described, it belongs to the seller. (You should not, by law, both keep the item and fail to pay for it. If you are fully refunded, that item should go back to the seller.)
There's a caveat to that, though. If the item is so damaged that the seller cannot resell it, repair it, etc., or if it cannot be packaged safely (for example, a shattered glass window), the seller may well tell you to please dispose of the item - i.e., they rescind their interest in the item.
Furthermore, the rules of distance trading are myraid. Some say it's the buyer's responsibility to pay the cost of returning faulty goods; some say it's the seller's responsibility. It comes down, I suppose, to a few different factors. Is the seller willing to pay the cost of the item being returned to them? (I am assuming that when you say you received "full refund inc postage", that is NOT referring to return postage.) Is the seller's location in Australia? How much would the postage be?
As you mention that you won a case, presumably you are speaking about either eBay's Money Back Guarantee - or you may mean that you won a claim through PayPal.
THIS is what eBay have to say about returning an item / return postage cost.
"Who pays the cost of return postage will depend on why you're returning it, and the seller's return policy."
"If you're returning an item because it doesn't match the listing, or arrives damaged or faulty, then the seller is responsible for the return postage costs."
Read the information on the link above for full details.
Thank you
