Providing consumers the opportunity to make installment payments for items that range in value from $100 to more than $10,000 is the business of Affirm, an online acceptance mark. The company has contracts with more than 700 U.S. merchants. Customers are mostly people who do not have the option of using a credit card or do not want to use one. They provide their name, birth date, phone number, and the last four digits of their Social Security number to Affirm, which uses traditional and nontraditional databases to handle underwriting. Affirm’s proprietary scoring models for personal data, me...