Well, we just starting charging apartment brokers in NYC for apartment rental listings, looks good so far, overposting may have already gone away. Volume has dropped a lot, quality higher, really good.
As expected, some brokers started posting in owner, and with volunteer help, we've been shooting 'em down. Similar problem in registration fee, but people know that's a low priority source.
Also, I'm finding that most of the problematic brokers have gone away, people who do stuff like posting fee ads in no fee, or who flood the no fee section for big buildings.
I do suspect to see more attempted bait and switch, and am already planning on how to pursue that.