If false advertising is unethical, then almost all businesses are unethical when it comes to customer relations. False advertising is very common. For example, right now, businesses can label their products "natural" even if they're not natural. There is no supervision of this term on labels, so almost everyone uses it now. If one checks the ingredients list of these products or calls up the manufacturer to find out about how the ingredients are processed, one will realize that it's far from being natural.
Although false advertising upsets us consumers, we are getting more used to it and many of us don't really do anything about it.