You have to remember that most people in early American were not able to read and write the English language. Census workers, judges and etc wrote down the name the way it sounded when spoken by the person involved who in most cases were not able to read and write. You see the same persons name spelled differently on various records. It just depended upon who was writing the name down. Certain and Certin were mainly used only in early times. The name then begin to be spelled Sartain and Sartin.