I purchased an item at 1.43pm Qld time today.  I had purchased the wrong item.  At 1.48pm, I requested cancellation of the order.  Within about a minute or so, I received a message from Ebay telling me that the sender had refused to cancel the order because she had already posted it on 12 October!  I had a lengthy chat with Ebay, who could not resolve the issue and told me to contact the seller and request a refund.  I contacted the seller, who advised me that she tried to cancel the order but Ebay would not let her because she had already posted it on 12 October.  She did not even list it until 13 October.  I have now raised a dispute with Paypal, as far as Ebay is concerned, they can do nothing as the item has already been posted!!