A real estate broker or a real estate agent is a person who represents sellers or buyers of real estate/real property. While a broker may work independently, an agent must work under a licensed broker to represent clients. Brokers and agents are licensed by the state to negotiate sales agreements and manage the documentation required for closing a real estate transactions. Some brokers and agents are members of the National Association of Realtors (NAR), the largest trade association for the industry. NAR members are obligated by a code of ethics that go above and beyond state legal requirements to work in the best interest of the client. Buyers and sellers are generally advised to consult a licensed real estate professional for a written definition of an individual state's laws of agency, and many states require written disclosures to be signed by all parties outlining the duties and obligations.
Generally, real estate brokers/ agents fall into four categories of representation:

Seller's Agents, commonly called "listing brokers" or "listing agents," are contracted by owners to assist with marketing property for sale and/or lease.
Buyer's Agents are brokers or salespersons who assist buyers by helping them purchase property.
Dual Agents help both the buyer and the seller in the same transaction. To protect their license to practice, a real estate broker owes both parties fair and honest dealing and must request that both parties (seller and buyer) sign a dual agency agreement. Special laws/rules often apply to dual agents, especially in negotiating price. In dual agency situations, a conflict of interest is more likely to occur, typically resulting in the loss of advocacy for both parties .Individual state laws vary and interpret dual agency rather differently, with some no longer allowing it. In some states, Dual Agency can be practiced in situations where the same brokerage (but not agent) represent both the buyer and the seller. If one agent from the brokerage has a home listed and another agent from that brokerage has a buyer-brokerage agreement with a buyer who wishes to buy the listed property, dual agency occurs by allowing each agent to be designated as an "intra-company" agent. Only the broker himself is the Dual Agent.
Transaction Brokers provide the buyer and seller with a limited form of representation but without any fiduciary obligations. Having no more than a facilitator relationship, transaction brokers assist buyers, sellers, or both during the transaction without representing the interests of either party who may then be regarded as customers. The assistance provided are the legal documents for an agreement between the buyer and seller on how a particular transfer of property will happen.A real estate broker typically receives a real estate commission for successfully completing a sale. Across the U.S. this commission can generally range between 5-6% of the property's sale price for a full service broker but this percentage varies by state and even region. This commission can be divided up with other participating real estate brokers or agents. Flat-fee brokers and Fee-for-Service brokers can charge significantly less depending on the type of services offered.