Great posts!
First off, I am mostly talking about the people who just completely vanish (we call it "pulling a Carson").
If someone is a man (or woman) about it, and admits they lost their job the next day (or more likely, lost their head in the auction) then I tend to give them one more chance. But we super-carefully document it and there is NEVER any further chances. AND I keep them on a tight leash.
The ones I am more talking about are like Carson himself. They completely vanish, and then two or three years later, when they are tired of solely buying from anyone but us, then send a message that they are sorry about what occurred, and that they promise to be good. Of course they know I have long since re-auctioned the items, so there is no penalty for them.
I DO evaluate these on a case by case basis. I just wanted to hear your thoughts.
We DO maintain over a 99% collection rate, and I know that is mostly due to bidders knowing that they CAN'T simply re-up (as they can just about everywhere else) and due to them knowing they risk a lifetime ban.