"(4) Real estate broker - a duly registered and licensed natural person who, for a professional fee, commission or other valuable consideration, acts as an agent of a party in a real estate transaction to offer, advertise, solicit, list, promote, mediate, negotiate or effect the meeting of the minds on the sale, purchase, exchange, mortgage, lease or joint venture, or other similar transactions on real estate or any interest therein."
Taken from the RESA Law. If a Client cancels the transaction, there is essentially no "meeting of the minds". Hence, the agent/broker is not entitled for the commission BUT it depends on any agreements made with the agent/broker (and if you wish to give him something for any 'financial gains' e.g. reservation fee or down payments made. [I personally experienced that situation, and I did not ask for commission].