This is the quintessential Sherman Act (15 USC sec.1&2) case. The same issue was decided several years ago by the Supreme Court regarding Multi-List Service realtors charging an agreed upon commission rate. Any agreement to either fix, peg or any subterfuge thereof to coerce prices or commission rate is a Section 1 violation because it is an agreement (conspiracy) between or among ostensible competitors to restrain trade or commerce and reduce the competitive environment in a specific market. It limits the consuming public in its ability to shop for the lower price in the same service or commodity.
The DOJ-Antitrust Division should pursue these clowns and clean up the local real estate market so that home buyers and sellers get the benefit of a competitive market.