There was a study done that, contrary to what you would think about incentives for the seller's agent, Both agents are more motivated by moving quantity of product.
In other words, they would rather buy/sell two houses at 20K less than work hard to get that extra 20K, but sell one less house.
The agents only make at most 1.5%, unless they are their own broker. So their profit of 1.5% of 500K is $7500. The fee of 1.5% of 480K is just $300 less. Not worth the time and effort. They'd rather spend it trying to sell another house.