Does the sentence below refer to visitors of a barber shop or to barbers themselves?
Bad guys shave here.
Could you explain the rule that governs such expressions ?
This is unambiguously active, but it is nonetheless ambiguous, because shave may be transitive, designating the act of shaving another, or intransitive, designating the act of shaving oneself. Consequently the sentence may mean that this is a place where barbers who are bad guys shave their clients (the Patient/Direct Object of the verb being inferred) or a place where men who are bad guys shave themselves.
The passive would entail the transitive sense, but it would require the verb to be expressed as BE shaved, with the Patient cast as Subject:
Bad guys are shaved here.