International mail

[mart_the_tart]

On my listing I include a disclaimer stating that an international buyer can pay economy mailing or tracked and signed mailing.  Tracked and signed is £3 to £4 pounds more than economy.  I add that if the buyer selects economy then I cannot be held responsible if the item goes missing.  I always obtain a proof of posting as well.
So a buyer has now "claimed" an item didn't arrive and wanted a refund.  I explained the entire situation, but as a kind gesture I refunded the cost of the goods and not the mailing charge.  I also sent them a picture of the proof of posting.  They opened a case and Ebay have decided to give them a full refund despite my disclaimer and proof of posting and that the buyer had a choice of how the item was sent.  Ebay state that "I could not prove I'd mailed the item,"  So whats a proof of posting then?  Also I'd like to know how Ebay knows that this buyer hasn't received the item and is just lying.  The buyer claimed to me "that this has never happened before" yet a look at their feedback shows a different story.
What rights do Ebay have to steal my money and now what do I do to get that money back?