If buyer opens a NOT AS DESCRIBED CASE, whatever you msy think you should provide a reply paid label, and on return refund. Only then can you report abuse of the system to ebay, who no doubt will do nothing.
By not dealing with it yourself, you have nothing returned, owe ebay money and if you do not pay up, ebay use debt collectors, and you will also have to pay their fees.
I am afraid that is the way ebay works.