Any agreement entered into subsequent to the first day of July, 1949, authorizing or employing an agent or broker to purchase or sell lands, tenements or hereditaments or any interest in or concerning them, for a commission or other compensation, shall be void unless the agreement, or some memorandum or note thereof shall be in writing and signed by the person to be charged therewith, or some other person thereunto by him lawfully authorized. No such agreement or employment shall be considered exclusive unless specifically so stated therein.