One lady bought an item from me and then sent an email that she wanted a matching set of four. Of course I only had the one that was listed, so she asked me to cancel her purchase. Not possible, of course, so I had to go through the invoice reminders/negative feedback process to get my FVF fee back. She was not happy. As a person who sometimes makes mistakes because of careless reading, I understand that this can happen. I changed her feedback to neutral later, because she did communicate with me and I knew this was not a malicious act.
I think this would be a good option to have in these rare cases. There's a big difference between someone who buys something and disappears, and someone who made an honest mistake.