Like Scarecrow said, people are banned for various reasons. If some one ripped off another person here do you really want them around your gear unsupervised? There have been people who have been banned for being ass hats and they have come back at later times under a different sign on. We often know about these people and as long as they don't act as asshats again we some times let them stay. Many of these people suffer from internet asshat syndrome and in face to face situations they're as nice as can be. I don't know what that says about a person who has a dr jekyll/mr hyde personality when they switch between off line and on line, but for the most part you don't see trade issues with those people.
As for being banned from games for the way you behave online, it has happened, I have a short list of people that it's happened to but it doesn't happen often. I've witnessed people excluded from games because they acted like a 12 year old on ASC. I've also witnessed people being banned from attending a game/club because of what they posted on ASC or other sites.