In the absence of laws requiring you to accept a co-signer, according to RentPrep, it`s up to you to determine what`s most useful for your property. Whether you are a landlord or a tenant, a co-signer agreement in a rental situation is useful if there are questions about the tenant`s financial situation. With the Co-Sign Agreement signed by a financially secure third party, the tenant and landlord have a safeguard that agrees to take financial responsibility for the lease if the primary tenant cannot pay for any reason. Add a co-signer contract to your lease or lease to prove that a co-signer has agreed to take financial responsibility if the tenant is unable to make payments.. . . .