If you sell your property subject to a seller carryback, you should get a promissory note stating the amount of interest on the amount financed as well as its due date secured by a first mortgage or trust deed recorded on the property.Since you have sold the property to the buyer subject to a seller carryback, you will not longer be on title to the property and would have no responsibility concerning it unless you have to foreclose upon it and take back legal title.You could report the buyer's payment on a monthly basis to a credit reporting agency. Whether the agency reports upon the payments internally depends upon the agency's custom and practice.In order to become a financial institution is a very complicated process requiring significant assets and statutory approval.I suggest you consult with a real estate attorney concerning any further questions that you may have.Good luck.