Your Tenant Rep will be your best weapon at every turn. He/She must have solid negotiation skills and be detail oriented. Don't be swayed by "full-service" large brokerage companies. You don't need property management skills. You need a person with a poker face. Interview several Tenant Reps, discuss your requirement and select one. Your relationship should be exclusive and in writing. The fee ideally should be covered by the landlord. Make sure the prospective Tenant Rep is absolutely aware how leverage is created for the Tenant.
Having an exclusive agreement will tell the landlord that you are serious enough about your renewal or relocation. Tenant Reps get compensated on deals they do; this is their only form of payment. The agreement must demand that any outside compensation to the agent, like a trip as an incentive, be disclosed. It is best to abandon all that and focus solely on a fixed percentage fee. The agreement with your agent should be submitted to the landlord and agreed to, and attached to the lease as an Exhibit to protect the agent's fee. Allowing your Tenant Rep to issue a press release to the local news papers will be noticed by a great many landlords. Landlords making contact with your Tenant Rep first is an excellent way to increase your options and take advantage of their concessions. In real estate deals, everything is usually on the table for negotiation.
Landlords and Developers negotiate on every possible economic component in a lease. The rent gets negotiated down, the Tenant Improvement Allowance gets negotiated up, free rent is obtainable, moving expense allowances are offered, parking costs are abated, and existing leases are taken over. Having an aggressive office Tenant Rep by your side for three, six, twelve or eighteen months is wise. We only get paid by what deals we represent.
As the tenant, you have every right to demand your Tenant Rep is fairly compensated for their efforts. If the landlord is either too cheap to pay the appropriate fee, or too arrogant, then walk away. This kind of Landlord will bring you nothing but anguish. If the Landlord is cutting cash so close, you probably should consider his financial stability.
Use a good strong tenant representation agreement with your agent, establish the fee, have this agreement submitted to the landlord and agreed to (AND attached to the lease as an Exhibit to protect your agent), or walk away. The Tenant is the engine that drives the Landlord. The Tenant has all the leverage.