Buyer claims item marked

[rid3333]

Good morning, 

I hope that someone can help me, please? I had a buyer contact me saying a baby outfit I sold them has pen marks on it, even though the outfit was packaged immediately after taking photos for the listing (including close-ups of the motif, where the buyer claims the marks are located) and I keep all stationary well out of reach of my 1 year old (who only plays with crayons and is constantly supervised).

The buyer hasn't asked to return it or anything like that, just said they're disappointed. I don't know whether to offer a partial refund if she wishes to keep it; offer a full refund if she wishes to return it (provided it's in the same condition I sold it to her); or ask for photos so I can see the marks myself as to my knowledge there were no marks (or do all three in one courteous and sympathetic reply). Including p&p it was £10 and sold as used, it was delivered about a week ago and this is the first time I've ever had a disappointed buyer; so I just want to make sure I deal with and word everything correctly. Thank you 😊 xx