Bans are done by Ihub Admin for violations of Terms Of Service.
Named moderators have no power to ban. I've never been consulted on a ban. Never had a ban explained to me.
Named moderators have no way of knowing if a poster is limited, but I would interpret a one post per day limit as a stern warning. If bad posting behavior continues, user gets banned.
If you look at the banned list, most are fairly obvious; duplicate accounts, insult/troll accounts, a single over-the-top offensive post, retweeting a banned user repeatedly, etc.
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