Final answer:
The commission in a listing agreement is determined by mutual agreement between the seller and the real estate agent or broker, not by external entities like local boards, state statutes, or real estate commissions.
Step-by-step explanation:
The amount of commission set in a listing agreement is determined by B) Mutual agreement between the parties to the agreement. This means that the seller and the real estate agent or broker will negotiate and come to a consensus on what percentage of the sale price will be paid to the agent as commission for their services. Local boards or associations of REALTORS®, Maryland statute, or the State Real Estate Commission do not set commission rates; these are typically a matter of negotiation between the seller and their chosen representative.