What was your intent? Did you intentionally create the entry to confuse or mislead the eBay buyer? I don't think so. Contact the buyer and tell them what your intentions were in photographing the cards together. Explain to the buyer that you too can understand how the photo can be misleading and that is why you described the single card up for auction in great detail below the photo. To conclude, I would say that if the buyer had any confusion about the auction or questions that he/she could have contacted you before the auction ended. Tell them that you are interested in continuing as an eBay seller and that you will consider changing the way you photograph items for future auctions and that you appreciate their understanding in the matter. And then let it go.