I've thought it remarkable that the realtors have gotten away with this
for as long as they have. It looks exactly like pricing fixing and
trying to lock out competitors, which if any other industry did it,
they would have the FTC and DOJ all over them.

As for state restraint of free trade, here in NJ I saw one a few years
ago that was remarkable. A local radio station had a promo going where
a gas station was selling gas at a deep discount. The state officials
show up and close them down, because there is a law in NJ that you
can't sell gas for less than cost. Now what's more remarkable is that
somebody in NJ govt was there in a few hours to enforce a law that
almost no one even knew existed.