There should be two brokers: one for the buyer and one for the seller.  They should not be from the same office or even with the same firm.  The  buyer and seller are adversaries haggling over price.  The regulator should track the opposite sides of transactions to insure that two agents at different firms are not acting in partnership.
The double dipping practice is so abusive of consumers that the Ontario legislature should amend the statute to settle the matter in the interests of both buyers and sellers.