Just as a point of fact, and for future reference, based on what the buyer has said about the bra, they do not have a right to a refund for change of mind (unless your listings said you'll accept them, which you didn't so that's not an issue).

If the buyer opens a request and selects a change of mind reason, you can decline the request if you would like to and eBay will not force a return or refund.

If the buyer thinks not liking fabric type / feel or how something fits = faulty, they might benefit from being pointed in the direction of a consumer site that shows these are not considered faults, but amount to change of mind.