The TLDR on this piece is that since commission is a fraction of sale price, the primary incentive for agents is to just get a sale, and fast, rather than maximise sale price, as even tens of thousands extra adds only a little to their cut, so their time is better spent pushing the property through the sales pipeline and moving on to the next one as quickly as possible.

There's a study which draws similar conclusions:

> 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.

https://www.nber.org/papers/w13796