First came the wildfire. Then came the scams.

Three days after the Mountain Fire tore through the hillsides of Camarillo in Southern California last November, Craig Crosby was at home assessing the damage when he spotted two men canvassing the neighborhood. Crosby’s house was still standing, but the blaze had burned down the northwest corner of the structure and his avocado orchard. Every surface was covered in ash and soot. The windows had melted, the doors were scorched, and everything reeked of smoke. The men eventually made it to his doorstep and introduced themselves as franchise employees of...