No real estate broker gets the absolute best possible deal for a client. They get a small percentage of any deal. A slightly better deal might be worth thousands of dollars to the client but only a few hundred to the broker. It's not worth the broker's time to spend a full week looking for the absolute highest buyer. It's in the broker's interest to process more deals more quickly than to squeeze that last little bit out of every property.
That's just the way it is.