Priscilla Rodriguez, an overnight stocker at a Walmart, has a strategy to protect her credit score as she and her husband look to buy a house.

The Sunland Park, N.M., resident uses installment loans from Afterpay to buy groceries, her pricey skin-care products and art supplies for her 10-year-old son, which keeps the balance on her two credit cards low—and the credit agencies in the dark.