The sentence is in past continuous. We use was/were + the -ing form of the verb. We generally use the past continuous to talk about actions and states in progress (happening) around a particular time in the past. It can emphasize that the action or state continued for a period of time in the past.
In the given sentence, we have used subject-verb agreement.
In subject-verb agreement if the subject is singular then the verb should also be singular. If the subject is plural, then the verb should also be plural.
Here, 'company' is a singular entity and hence, we have used 'thinks', a singular verb.
A man who always . . . . . . . . at the faults of his children is their worst enemy.