A guarantor agreement is an agreement of a third party to provide assurance of payment in the event the party involved in the transaction defaults. Fill out the lease guaranty application online and send us your paperwork.A form of guarantee agreement is an agreement where a guarantor promises to fulfill the financial obligation of a borrower if they fail to pay. This document is a guarantor form for a white Toyota Corolla vehicle. Get expert advice and clear guidance for tenants and landlords.