Buyer claiming there's marks (no personal info)

I sold a pretty much brand new satin look sky blue steel boned corset on vinted.

I bought it in person and it was pretty expensive but I wore it for like 3 hours and then COVID hit and I never wore it again and it no longer fits. I sold it for £40 which was at a £10 discount to what I wanted and had it on for.

I photographed every part of this item and checked it over again before I put it in the postage bag etc and the seller has left feedback saying it had marks I didn't advertise? I genuinely don't think there's a single mark on it and I've asked where they are because she got an absolute bargain to be honest and it had a lot of photos included as well as me checking it again with it being a light colour material.