I don't trust ebay international standard delivery anymore. I am a US
seller. Ebay didn't keep record for the domestic tracking number on
record if you don't keep it yourself. If ebay ship center lost your
package I can't see anything. Then the buyer...
Did you have a receipt from post office? It will show the weight and
time of the shipment... Email it to PayPal. If PayPal still refund to
the buyer, get a police report. That is all you can stop scamer online.