Input needed on a developing ebay buyer situation

[hcv123]

So I sold a PSA graded card. The buyer received the card and is claiming the card I sent is other than the one I had listed in the auction. He sent me an image of the same card with the same grade (clearly no where near as nice as the one I sold him), claiming I sent him the wrong card and is demanding I send him the correct one or a refund. He has already sent 7 emails and requested a return through ebay.

I double checked the group of cards (not a large one) I have listed, just to make sure I am not missing something. I own no other cards that are the same card and grade. I plan to call PSA to further confirm some details (1 - I believe I had the card I sold graded myself and it has been in my possession since and 2 - to see what I can find out about the card he is claiming I sent (which I never owned). I just sent him an email trying to gently call foul and encouraging him to not take this further. The only thing that is giving me any pause is he is an ebay user since 2014 with 526 positive feedbacks.

Here is the original transaction:

https://www.ebay.com/itm/151874336412


Your experience and suggestion(s) are appreciated.