> the vast majority of their compensation comes from the house getting sold at all, and the gain from anything beyond that is weak

You might find this study[1] interesting:

>Our central finding is that, when listings are not tied to brokerage services, a seller's use of a broker reduces the selling price of the typical home by 5.9 to 7.7 percent, which indicates that agency costs exceed the advantages of brokers' knowledge and expertise by a wide margin.

[1]https://www.nber.org/papers/w13796.pdf