How do you level the playing field in this case? One account has 50% disallowed items (50 of 100) and another account has 0.005% disallowed items (50 of 1,000,000). You could bias _against_ large accounts by banning when they reach a fixed number of disallowed items - but then you let little guys (or any big guy that makes lots of small accounts) skate by under some arbitrary limit.