Agency Broker

A broker that acts as an agent to its clients. When acting as the agent, the agency broker must look after its clients' best interests, which involves attempting to fill client orders at the lowest price and in the fastest way possible. Common clients of an agency broker include large institutional funds that place large block orders.

Investopedia Says:
An agency broker is a broker that acts as a middle man to the stock exchange, and places trades on behalf of clients. This is in direct contrast to broker-dealers, who purchase orders from clients and then sell these blocks into the market. Special care must be taken when using any broker, as there may be hidden fees associated with placing trades.

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