I am pretty sure that doing that violates the Fair Lending Act...and all kinds of other things. There may be some grey areas involved since the act pre-dates Facebook, but if someone did that to me, I would certainly make it a "cause celebre" and go after the collection agency/dealership with a vengeance.
Whether a debt is valid or not, the lengths that some collection agencies go to, to attempt to collect are blatantly illegal and they should be seriously shot down. There are plenty of legal remedies available to creditors/collection agencies, they do not need to resort to illegal ones.