Earlier quoted context omitted.
It being % based means the incentives of the agent are more aligned with the seller than buyer. If the agent charged a flat fee -- the agent doesn't have incentive to negotiate a higher price.
There was a Freakanomics podcast episode or book section (I don't remember) where they asserted that the data showed realtors left their own homes on the market longer, ultimately yielding a higher sale price, when compared to homes they were selling for their clients. The reasoning they gave was that the difference in the realtor's percentage between a lower total price and a higher total price was not meaningful en…
Real estate agents are more likely to plan sufficient time to maximize sale value; most people make plans with timelines where sale (or purchase; I bet you’ll find a similar issue on the other side, too) of the house is a blocker for other things before talking to an agent, so the disruption of not completing the transaction timely is significant.