If a rental listing is in the MLS, then the listing broker is required to pay a commission to a cooperating broker. That doen't mean that all transactions work this way. If an agent isn't being paid by the owner or landlord the commission can be anything from a half months rent to 15% of the yearly rent. In NYC more often then not the tenant is paying the fee and this is frequently 15% of the yearly rent. All commissions are negotiable.