It might be, but what you're gonna do, sue them from behind the counter? You probably don't even have independent (i.e. not relying on their website) proof that

It might be, but what you're gonna do, sue them from behind the counter? You probably don't even have independent (i.e. not relying on their website) proof that's what the site said... But even if you do, how many people would bother? Eventually, somebody would launch a class action, but by then clever marketing person who launched that promo would already be promoted.