In most cases, I consider a transaction good if:
I offer something, the person pays for it, I send it, they get it and are happy with it.
OR
Someone offers something, I want it and it's available,I pay for it and I get it and it's as described - life is good.
I usually try to leave feedback - sometimes I don't - It's nice to get give and get good feedback.
I usually don't even get overly upset if someone changes his/her mind about buying something - as long as the person lets me know, too!!!!!! (There have been a couple of major exceptions to that, but if it's a piece that I have not cut yet and something comes up in the other person's life - stuff happens - just let me know, too. )
I would like a way to let others know that someone has not followed through for no good reason, though. (Note - I am allowing for illness, accidents, death, loss of work, etc.)
Overall, MOST of the people I've dealt with have been great - either buying or selling - and I would be happy to work with them again.