I recently sold a Microsoft office key, which was factory sealed. A buyer purchased two and claimed they did not work. This is incredibly unlikely, as I’ve sold about 20-30 of these across two eBay pages. He is the first buyer to report this problem. What a coincidence that his codes are the first to have this problem, isn’t it? He is now attempting to get me to pay return shipping on two useless items. He has shown no proof that they did not work, and now he is ignoring my messages. These codes are a one time use. He is 100% trying to scam me. What can I do to avoid losing money?