People can get banned without having openly offensive posts.
Sometimes it's a trading dispute or stuff that's said via PM (threats, insults, etc). Sometimes it's just because we find out it's a new account from a member who is already banned.
Also, sometimes we will remove posts to clean up important or informative threads. If a member steps out of line so much that a ban is warranted, cleaning up the thread can remove the offending post and make the "show all posts by this member" list look all clean.
As you see, there are plenty of reasons why people can be banned despite looking okay.
Some members, although banned from other sites, can walk a fine line for a while, meaning they're rude enough to get a few slaps on the wrist or a temporary ban ... but just not rude enough to warrant a permanent one.
Eventually they WILL slip up though, and then the appropriate measures will be taken. But just because someone isn't banned, doesn't mean he/she is not in the moderators' crosshairs.
As for you reading posts that you feel are unacceptable : We can't read every single post, so some may slip through.
If a post is really offensive, hit the "
" button on the bottom right of that post and fill in the report form. That way it'll certainly be read. Just don't abuse that button because that might backfire.
What happens after you submit a report (especially regarding bans, cleaning, etc) is at the moderators' discretion. We can't/won't explain our every action, so it's best not to go too far into this.