Buyer is claiming a dress she purchased from me in VGUC came with a pretty big stain on the front bottom. I looked the dress over before I sent it and didn’t see the stain. There is also not a stain visible in the photo I took on the same day that I shipped the dress out. At first she wanted a partial refund of 50% back but now she is saying she wants a refund plus shipping fees tonight and that she will ship the dress back tomorrow. How should I proceed with this? I’ve made many transactions and have never had an issue with anyone before.