Just to clarify, we don't have any banned accounts. I was asking the question to try and figure out why we don't, really - because we've played in some murky water and the worst we've seen is a slap (more like 10-15 slaps)... but all over approx 3 year period and never more than a couple slaps per MCC account before we open a new one.
I should have known that it wasn't the piddly pre-pay balance holding the doors open but I had to ask.