Thank you for using our forum. My name is ***** ***** I hope to assist you today.
I am very sorry to learn of this situation, your buyer has taken an extreme stance on this situation.
Unfortunately your only recourse here is to simply defend the court case that was filed against you.
If it was filed in the wrong county (they likely filed it in the court where they lived), you can take a very aggressive (high risk) approach and ignore the suit, and when he gets his default judgment and tries to collect, you can claim the judgment is unenforceable as he was in the wrong venue. The downside to this is twofold: (1) you will have a judgment entered against you; (2) your strategy relies on the court agreeing with your interpretation of the venue argument (these online sales cases are not exactly 100% clear), and if you lose the venue argument, you will have lost the opportunity to defend the action on its merits (so you will owe him for whatever damages he was able to prove).
You can appear in the other court for the sole purpose of contesting venue and try to move it to your county. This is a much less risky approach.
Or, you can appear in court there, and simply defend the action (based on what you posted, it appears you have a high likelihood of prevailing, you have a consumer who is simply upset with the product they purchased not fitting what they wanted to do with it - nothing wrong with the product itself.
Unfortunately, the dispute resolution with eBay is not going to have any bearing on the civil action other than to give you some additional confidence in your case.