Ebay can only step in AFTER you have opened the Correct Case, which is NOT AS DESCRIBED. If seller does not respond ten after 8 days the option to escalate to ebay appears and they take over. Seller gets penalised for not dealing with the case themselves as they still pay the selling fee even though they are forced to refund.
If you just opened a return case, then a private seller can decline, and there is nothing more you can do through ebay. However you can open a Not as described case with paypal.