The key documents in a seller financing transaction include: (1) Purchase Agreement; (2) Promissory Note; and (3) Deed of Trust. We'll discuss seller financing for business and how it works, as well as highlight the pros and cons for both buyers and sellers.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 buyer must complete Form 593-I, "Real. Estate Withholding Installment Sale Agreement. A business purchase agreement is a legal contract specifying terms for buying or selling a business, including conditions and obligations.