How can my buyer remove the negative feedback he left on a transaction error on his part?

[enterprisesalesforce]

I sold a pair of sneakers. The listing clearly said "no returns" and clearly listed the size as Size 12. The buyer got them and then left feedback that said "I received size 12. I need size 7.5 or 8". After leaving negative feedback, he requested a refund which I declined. He then contacted his credit card company and asked them to refund the money he paid me via paypal. They contacted paypal and paypal not only refunded him the money, they also charged me $20. The buyer did return the snekers to me in the mail. But I am out $20 plus shipping. I emailed the seller and told him I would let it all go if he would just remove the negative feedback. However, when I click on "feedback revisions" it says "None of your Feedback is eligible for revision"

I already reported this buyer to ebay, but to be fair, he had never made a purchase on ebay before and he really probably didn't understand how it worked. I am not blaming him, but this result (losing money and getting bad feedback that can't be removed or changed) is just insane.

Any help would be appreciated.