This is a tough situation because right now you're on the hook to take a hit on your metrics over the not as described claim, so I get why you're frustrated. But I wouldn't agree you handled the situation as well as you could have either.
You stated ebay found the case in the buyer's favor, and that their claim for not as described was invalid (sounds like it was).
The problem is, you're setting yourself up for problems with your return polices, and more so your mentality towards your buyers. You don't accept returns, which is enough to make buyers apprehensive to begin with. A lot of people view this as "if there's a problem with your order, I'm not willing to help." And let's face it, this isn't the greatest mentality to have as a retailer.
If you don't want apprehensive buyers, then make them feel like they can trust you. Anytime a buyer isn't happy, I tell them to return it, here's your label. I do other positive things like leave feedback right after printing their label too.
While its true that many will lie about the reasons for their returns to avoid the shipping costs, you're greatly increasing the likelihood of getting hit with not as described claims. Many buyers will sooner message than open a return case, which helps to avoid dings on your metrics. But they often wont do this if they think you're going to put up a fight.
You also did the right thing to report the buyer for lying about the reason for their return. But you messed up by not accepting that return. ebay will almost always refund when a seller refuses to accept returns.
All being said, I avoid a lot of problems with buyers, and ebay itself, by simply offering 30 day returns, and when they aren't happy for any reason, I will always accept a return no questions asked.
Its better to focus on ways to drive more sales than to waste time fighting returns.
