What Mazin just said.

The feedback section is a tool that everyone can use to see if they want to invest time or energy (or money) into trying to put a deal together with someone. That's what it's there for.

If someone is unreliable or even if they are just generally a douche bag in real life as long as they obey the rules here I see no reason for any sort of ban.

I keep a short list of people here that I won't deal with for one reason or another. Some of those people even have a good track record of positive feedback but it doesn't mean I have to choose to deal with them if I don't want to.