There are process (ser) and status (estar) passive forms. I do not quite catch the difference in meaning and translations:
La casa es vendida
La casa fue vendida el mes pasado
La casa está vendida
La casa estuvo vendida
La casa estaba vendida
if the last sentences make sence?
Nomenclatures differ, but, generally: The passive voice is "ser" + participle. The the passive meaning is obtained using the passive voice, the passive "se", the passive third-person plural, the passive "tú", and by shifting the object to the head of the sentence. But to avoid writing a book, I'll stick with "ser" + participle and "estar" + participle. Generally, "ser" + participle describes an action, while "estar" + participle describes the state that results from the action.
La casa es vendida a menudo.
The house is sold a lot. [habitual action]
La casa fue vendida el mes pasado.
The house was sold last month. [past action]
¡La casa por fin está vendida!
The house is finally sold! [It was on the market for months.]
La casa estuvo vendida.
[This case is a bit odd and I'll pass over it.]
La casa estaba vendida.
The house was sold.
In the last example, I walked by the house yesterday and the "FOR SALE" sign had a "SOLD!" banner taped to it, indicating the new state of the house. I have no idea when the sale happened.
Notice, by the way, that there is no "estar" passive meaning. In the above examples, "estar" functions in its usual way, and "vendida" functions purely as an adjective.
This would be the standard passive voice in present tense. If there is no explicit agent, it is more common to use the passive reflex form:
La casa se vende.
But it's ok to say:
La casa es vendida por sus dueños.
Standard passive voice in past tense, totally ok. You can also say:
La casa se vendió el mes pasado.
This may happen during the process of selling a house: you see an ad for the house, call the real estate agent and they respond with this phrase, meaning that there is already a buyer for it. Note that this is not passive voice, but a state of the house. Buying a house is usually a lengthy process. Once it's finished, it would be more appropriate to say:
La casa ya se vendió.
or
La casa ya fue vendida.
This can be used when there was a buyer for the house, but the sale failed for some reason:
La casa estuvo vendida, pero el comprador tuvo un problema de salud y la operación no se concretó. Ahora está en venta nuevamente.
You are telling something that happened when La casa está vendida was true. For instance:
Me dijeron que la casa estaba vendida, pero pedí verla igual por si el comprador se arrepentía.
or:
La casa estaba vendida, pero hice una oferta superior y me la terminaron dando a mí.
