In the US the seller pays for both the listing agent as well as the buyer’s agent. When you list your house, you agree to a commission for your listing agent and you advertise a commission to co-broke on the MLS listing, which entices buyers agents to show your house (or steer buyers away from it if the commission is low).

I think the biggest impediment to driving down costs to the consumer is the momentum of social convention.

Even for agents at fixed-cost brokerages, they know they can charge 2-3% so they do, and most people don’t know that it’s negotiable.