There are agents who purchase the goods from the manufacturer and sell them to the consumer. In a sense, such agents bring the manufacturers and the consumers together for transaction. The remuneration which an agent gets for his services in the transaction is called commission.
A broker is that middle-man who brings together a prospective seller and a prospective buyer and negotiates the sale between them. The commission that he gets is called brokerage, which may be charged from both the parties.