Presumably percentage is a proxy for how long it takes to sell the house. Assuming more expensive houses have fewer potential buyers and take longer to sell. Thinking about all the other ways they could charge I don’t know if there is a silver bullet. They could charge by the hour, which puts pressure on the buyer to not see a bunch of houses, and has all sort so implications for buyer and seller. They could charge a flat rate but then they would be a lot more careful in the types of houses they take on. Other oddities are that they get paid more when the house into market is doing well and presumably are doing less work and they get paid less when the housing market is doing well and are presumably doing more work. But yeah there’s a lot of easy sales subsidizing hard sales I imagine