What are my options when a case is opened against me on ebay?

[Iya]

If a case is opened against you, you have several days to work it out with them. If you are able to come to an agreement without refunding them then that's good. His selling it in eBay is one way of his resolving it on his own so he should not give you negative feedback if you reason that out with him.

If you're not able to work anything out with him then, you need to wait a few days to escalate the case to eBay. When you escalate the case, be very detailed, as detailed and direct to the point on what you sold and what they are claiming and all the relevant info you have.

However if he already escalated the case then you need to wait for the decision on the case before you can appeal the case if you lose.

You can also report him online in your My eBay Selling area like what the others commented here.

By the way, did you buy the card yourself or you had it autographed personally? If you bought it from someone you need to have the receipt to help you with the case.

And yes even if you win the case they can still leave you negative feedback so you need to really communicate well with your buyer. If you are able to make them see your point and if you're able to come to an agreement, you can send them a feedback revision request (once). Make sure you've had their agreement on getting the feedback revised if they already left you the negative feedback as eBay can only remove limited kinds of negative feedback.

I did write an article about selling in eBay 2 years ago, it's like a guide for new sellers. Just in case if you wanna read and if you're not very familiar with eBay yet, you can check it (as my source) below.