Should I just eat this item and give a refund

[crazy4kinsler]

I sold a complete, sealed set to a buyer on eBay about a month a half ago. It wasn't an expensive set (less than $50), but it was sealed. A few weeks ago, he said the cards were stuck together when he opened them. I told him I didn't have any way to know they'd be stuck together, and I suggested he freeze them to maybe help pry them apart. However, the buyer just opened a case last night saying he had opened the cards, they were sticking together, and he wanted a refund (didn't mention anything about a return).

The reason he gave is
"Doesn't match description or photos"

However, now they're not in the same condition that he bought them in as the set was sealed. And now it's been opened. Should I contact eBay and let them know the set is no longer sealed as how he got it? Or should I just refund? There is an option to just refund, however, I'm afraid if I do that, he'll leave me negative feedback. And I don't want that obviously.

What do the masses say? Refund and move on? Make him return and then refund? Or just just decline the refund?