Yahoo recently featured an article on how to detect misleading ads. It's an easy fact to forget as an ad industry copywriter who's faced every day with the technicalities of what makes an ad misleading or false how little the public really knows about the nuances we hold so dearly (the ones that keep us out of court).
I'm glad to say the article hit on one of the most important points- pay attention to the words. The words are almost always where actual claims are made that have to be substantiated. Vague statements are usually intentionally written that way because specific statements must be proven, and if can't prove you have #1 customer satisfaction in the U.S. (which you would have to substantiate with an independent study), it's much easier to say you make The Ultimate Driving Machine.
What I think the public may not know is the legally agreed-upon safe zone called puffery. Puffery refers to subjective claims that can be neither proven nor disproven. A good example would be, "The best burger around." Best could mean any variety of things. It could refer to temperature, flavor, value, etc. Around gives you no geographical reference. Because who makes the best burger is subjective, advertisers are allowed to make those claims without substantiating them, because it's impossible to substantiate the subjective. If the company said the make "The sandwich people prefer two-to-one," like Domino's did, they would have to substantiate it with legal disclaimers. If you pay close attention to the ads, you'll see them.
The confusing, and probably unfair, part of puffery is that there are so many words deemed subjective that sound definitive. Words and phrases like best, greatest, preferred, favorite, number one sound like serious claims, but fall under puffery; essentially a legal right to be boastful in a vague way.
It gets even more confusing when you realize that a company can take one of these claims and decide to prove it within ceratin criteria. For example, an auto manufacturer could make the legal claim to be the "Number One-Selling Auto Manufacturer in the U.S." and base it on total number of automobiles sold in a given time period, say the second quarter of 2008 to the second quarter or 2008 while another manufacturer could make the same claim of, "Number One-Selling Auto Manufacturer in the U.S."but defined as total revenue instead of units sold. They could even simply select a different time period if they beat the first manufacturer in that period.
I could give examples all day long, but I'll spare you. After all, several of my college courses had entire chapters, sections or even weeks of the course devoted to differentiating what constitutes false ads, legally misleading ads and puffery. Just to give you a peek at what we learned, false is not the same as misleading, legally misleading is not necessarily the same thing as practically misleading and what seems definite is often considered vague.
It's a complicated world out there, but if you stick to the basics above, you'll be a lot better off.