Shantee you are absolutely correct. You never have to pay an agent to help you do anything. Of course, many agents will require that you sign a contact with them. This contract directs them to assist you. One of the provisions of the contract is how the agent will be reimbursed for their services. The reimbursement clause usually states that any amount you might owe will be reduced by the amount that the agent receives for representing you from the listing broker.
Unfortunately, the majority of listing brokers in the DC area offer quite a reduced fee to agents that bring renters to property. Typically, an agent would expect to receive 50% of one month's rent. If the amount offered is less than that, the contract will dictate that you make up the difference.
There are many thoughts regarding why listing brokers allow this inequity. The end result is that many agents will not assist people seeking to rent. You will find it much easier to speak directly with the agent that listed the property. They will be delighted to help you (they will not and can not represent you ) hoping you meet the needs of the landlord so they can keep all of the commission.
Best of luck