Check your original lease contract. Most will have a provision for renewals by tenant and if the broker will be paid at renewal, etc. An example would be: "If tenant renews lease at end of term, broker (will/will not) be paid a commission of (percentage) of new gross lease." Where in most cases that I have been a party to, the commission due upon renewal (if any) is about half what the original commission was. In any case, even if the tenant no longer works with the broker, the contract is legally binding as per what the owner/tenant agreed to when the lease was signed. Additionally, I wouldn't allow a new broker to be paid on a lease renewal for an existing tenant. Unless there was some circumstance where they need an agent to renegotiate extraordinary terms, TI's etc., the tenant should be able to hash out a contract directly with the owner. Further, agents are paid because they BRING the tenants to you. If they are already your tenant, you shouldn't need to pay a new broker. That's ridiculous.
Sep 19, 2014