I would have called their bluff on one-ways between corporate stores, and then ask them if they'd rather have the convenience of you cancelling the reservation instead. Since it was a freebie, chances are they wouldn't have cared, or would have preferred that. This is one of many reasons people are increasingly double booking rentals with different companies, so they won't be in the lurch if a car is unavailable, or at the last minute something goes wrong.