I've had 3 cases over the past 10 months similar to this...
1 & 2. The buyers claimed the garments had "a loose thread" and they demanded a full refund. One was aggressive from the start, the other one started off nicely but when I politely suggested that I did not consider that one loose thread was grounds for a full refund, she exploded and became abusive.
In both cases, I let the buyer escalate the case to ebay, who immediately closed the cases stating the buyer would receive a refund, but not from me and my ebay account would not be affected. Yay.
3. The most recent case was about a very abusive and rather strange buyer who claimed a neutral, nice pair of shoes were "clown shoes" and ridiculous, damaged and bleached, etc and wanted a full refund. I again politely said I did not agree with any of this.
She grew more and more irate and abusive when I would not accommodate her, calling me rude names, saying I was stupid, threatening to leave bad feedback, and I said I would no longer communicate with her as she appeared to be irrational, and I would let ebay handle it.
When I saw she had actually left negative feedback for me (my first), I immediately went onto ebay live chat, explained the situation and they apologised profusely as they could see all her abusive messages, escalating to now using bad language even though I had stopped responding a while back. They said they would close the dispute in my favour in 3 days when the required time had elapsed, and would also remove her negative feedback.
Sure enough, the case was closed, she got no refund, and the negative feedback was removed. I bet she was livid. I wouldn't know though, as I blocked her.
So...have faith that sometimes ebay DO side with the seller!