Suspicious about buyer's claims

[#1]

Hello,

I recently sold a dress on eBay that had a couple of stains, which I clearly stated in my description. The auction ended July 29, and payment was received promptly. I shipped the dress 2 days after payment received.

Yesterday I have received an email from the buyer saying that the dress has "2 large" stains that were not mentioned in the description, asking for a partial refund.

I do describe my items carefully, have 100% positive feedback and am pretty sure I would not have missed this, apart from that the buyer has waited 10 days to contact me, to me she could have worn the dress in the meantime and stained it.

What would be the best way to resolve this? Any advice would be much appreciated.

Thanks