A broker or middleman was an individual who arranged sales transaction between a buyer and a seller, usually for a commission.
In 2370, Quark acted as a broker when getting people seats on evacuation vessels leaving Deep Space 9, though he used the acceptable Ferengi method of overbooking in the process. (DS9: "The Siege")
In 2373, Quark put up his bar as collateral to three different brokers. (DS9: "Business as Usual")
Thadial Bokar, a member of the Orion Syndicate, used the guise of a commodities broker in 2375 while dealing with the Tigan family. (DS9: "Prodigal Daughter")