I think this is similar to the discussion a while back about how to allocate quotas. At some point, the most effective solution is to say, "I am an arbitrary god and QOTO is my creation; if I wish to expel you, I am at liberty to do so." Access to the service isn't guaranteed unless we start paying for it.
Trying to publicly impose on yourself restrictions limiting your options to deal with troublemakers just offers an incentive to game the rules and look for loopholes.