When you rent from a real estate office do you pay the agent who showed you the listing?

Apparently people aren't really reading your question. No you do not pay a real estate agent when you rent. They do however receive a commission or bonus IF you were to rent the place but that wont effect you at all, they would get it from their employer (the real estate company).

the agent is usually paid by the seller or owner....if they are charging you as a buyer you would have to sign a contract...

No you pay to the Listing Broker Realty Company If the agent are one of the same, they will get full designated Selling Comission if not the comission will be allotted as per listing agreement . ( listing/ selling/ brokers)

The agent does not receive payment directly from the prospective tenant UNLESS the agent is receiving an application fee for services rendered in running the credit report, verifications, and background checks to determine the qualifications of the prospective tenant. Typically, the listing agent renders the services of qualifying the tenant, however, it can sometimes be the agent representing the tenant IF the lising agent assigns that responsibility to the agent representing the tenant.

Commissions are paid and received between broker and owner of the property and the amount is determined by what is agreed to in writing within the listing agreement.

Trust me. I've done more leases than I can count here in Texas. Double check with a local broker in your area as to how it works in your state. Always keep in mind, each state has its own real estate laws and guidelines. So make sure whatever is being told to you is applicable in your state.