Well it sure makes sense, doesn't it? It helps to know that those acne products they sell on TV are used by people we all recognize as NOT having terrible acne problems (I think Jessica Simpson and Vanessa Williams hawk them - and show how they look without them). I don't know that they have to be attractive, but they need to be a testimony to the fact that the product *works*.
I wouldn't take advice from a fitness instructor who had always been out of shape. I wouldn't pay for stock tips from a guy who doesn't have a fortune. I wouldn't listen to a football coach who never had a winning team. I wouldn't take nutrition advice from someone who didn't look healthy.
They might all be giving good advice, but they lack credibility. Because if you KNOW what a good stock is, wouldn't you invest your own money? Wouldn't your life SHOW you know what you're doing?
Ever wonder about the psychics who give winning lottery numbers? How valuable can THOSE numbers be? Wouldn't they be using a few THEMSELVES if they were worth a dime?
ON THE OTHER HAND -
I *will* listen to a doctor who has health problems - if he has the credentials to show he knows his stuff, and the testimony of reliable people - because health isn't something you can do much about sometimes. I will listen to a singing instructor or a music teacher whose gift has faltered, if there's evidence they were ONCE good - because age will overtake us all. I won't take advice from a gardener who can't grow anything but weeds. I will take advice from a craftsman IF he's *ever* made something beautiful.
I guess it just depends. Some things people can control, some things they can't.