Typically, this involves two documents: a financing agreement (basically a loan document outlining the details and terms of the loan) and a promissory note. The key documents in a seller financing transaction include: (1) Purchase Agreement; (2) Promissory Note; and (3) Deed of Trust.The "due on sale" clause is crucial to owner financing. Buyers and sellers should know the meaning and legality of this clause in agreements. The Seller and the Purchaser are sometimes referred to in this Agreement individually as a "Party" and collectively as the "Parties. You will need a promissory note and security agreement that addresses the key terms of the seller note.