The ad DID say "while supplies last." Caveat emptor. A savvy moocher would have known that this promotion would be a popular one and gone on the first few days to get their "free money."

You went in there with one week left in the promotion with no intention of even thinking about buying a car because you wanted to get something for nothing and you left empty handed and you're upset about it? You could have called beforehand and saved yourself a trip.