It's not just buying and selling, it's life in general. I really dislike unreliability. Of course, there's always the odd occasion when something crops up at the last minute which is completely unforseen, but some people make a habit out of it.
I know someone who's organised a 'group' activity a couple of times, with a fairly disparate set of people, several of whom I didn't know. I was asked to go to help out as I vaguely knew what I was talking about , despite the fact it was quite tricky to get due to work. Nevertheless, I made the effort and duly arrived.
On one occasion he bailed entirely, leaving me holding the proverbial baby. On the other, he turned up but I think he was more interested in the notion of the event and his enjoyment of it rather than the actual practicalities of running it. 'Detail', was something he left to some other sucker, namely me.
There won't be a third time...