I remember that class.
If you have an active real estate license and you get a listing agreement you can charge whatever commission the seller will pay. Now I've never been able to get more than 12% however, I was providing a number of addition serves in the terms of that listing agreement.
Price fixing is illegal so RE companies cannot charge a set industry price.
As a Realtor or licensed agent you owe the seller your Fiduciary responsibility.
http://www.efmoody.com/arbitration/fiduciary.html
The good faith has been interpreted to impose an obligation to act reasonably in order to avoid negligent handling of the beneficiary's interests as well the duty not to favor ANYONE ELSE'S INTEREST (INCLUDING THE TRUSTEES OWN INTEREST) over that of the beneficiary. Further, if the agent should find him/herself in a position of conflicting interests, the agent must disclose the dual agency (acting for two parties at the same time) or risk being accused of constructive fraud in regards to both or either principals.