EDIT: should say *buyer not *seller in title. I am seller.

I recently sold a retired, pre-owned set on eBay. I listed the set as 100% complete and went above and beyond with breaking it down and re-sorting it into the numbered bags from the instruction manual, which I've never seen an eBay seller do. I let the buyer haggle me to $75 off the listed price. I shipped it promptly and paid extra out of pocket for shipping because it ended up being more than I listed the shipping price for.

He received the set and messaged me tonight saying he did a "detailed inventory" and found 5 missing pieces (out of 3100 ). They're all extremely common pieces, not exclusive to the set or necessary to the structural integrity of the build in any way, and the total cost on pick a brick on the LEGO site is like 60 cents. He's asking for a partial refund since the set is "not actually 100% complete."

I don't think a refund is justified but I'm concerned that if I don't give in to his demands he will give me a horrible review or escalate a case to eBay because the item was "not as listed."

Any advice on how to handle this?