For Rebecca Harris, the little house she rented in Huntersville, North Carolina, in 2020 represented her escape from a toxic marriage, the beginning of a new life for herself and her children. Until the ceiling started caving in. Harris’s landlord was FirstKey Homes — one of a relatively new, and growing, class of single-family rental companies. FirstKey had bought the house in Huntersville in 2019, and leased it to Harris the following February. Over the next four years, the home was...