My advice? If the earrings returned to you are the ones you sold and are in the same condition they were when you sold them, count yourself lucky, take the small loss, and move on.
Yes, you can fight a SNAD. But is it really worth the time, energy, and money to have a jeweler test the earrings and provide a written report for eBay, go through the eBay processes, et cetera, when all you're out is a few dollars for return shipping? Considering everything else you're facing right now, is this the battle you want to pick?
This kind of return is a cost of doing business in America, where consumers have grown accustomed to "no quibbles and no questions asked" returns.
Whatever you decide to do, good luck.
