I feel like the point of negative feedback is to make traders aware of past occurrences with the individual, avoiding altercations in the future with unaware customers/traders.
If the feedback does not make this awareness, it is not assistive in those regards.
Also, It either wasn't explained or I don't see where you are inconvenienced. This makes it more similar to situation #1 - A krono buyer comes to me and says I'll take 10. I provide info, I get ghosted.
I was not inconvenienced, so I don't leave negative feedback.
I'm on nobody's side, and while I do agree that the "handshake" of a sale did occur, and in some ways might warrant some type of grey/red feedback because it is poor business practice, I can't draw a clear enough line to a definitive notion. We have seen similar issues with "bad business practice" that slides for a while, but when it is done repetitiously, the line is easier to draw and usually results in a red eventually.
Perhaps consider moving it to grey feedback stating the trade was accepted and the supplier backed out without letting you know, and explaining how you were inconvenienced. That would probably be more understandable to the community and still give a heads up to future traders.
In the end I play EverQuest. /shrug