Member Rara Avis
You need to distinguish, I think, between a patently false facade and one that is simply a less than accurate representation. The snake oil salesman (we presume) is purposely putting on a mask. He's trying to fool someone, usually for his own gain. Most people do exactly the same thing on a first date.
People not only don't give a true accounting of themselves in public, they almost always give a different accounting in different publics. You don't act the same way around your dad as you do your boss, and neither of them would probably recognize you at a bachelor party. Those are generalities of course, but I think the principle is universal. People always wear masks.
I'll agree with Chris that most people are wary of revealing everything to everyone. I'd carry it farther, though, and say that no one ever reveals everything to anyone. We all keep secrets. Even from ourselves. Sometimes, especially from ourselves.
What you're really trying to do, I think, is equate this facade with hypocrisy. Are they the same? Sometimes, but certainly not always. If I tell you that I don't drink and you walk into the room and see me with a champagne glass, it doesn't necessarily mean that I lied to you. It usually just means I didn't tell the whole truth, often because it's not important, more often because it would take two or three days to do so. Even if I was a teetotaler, I would probably toast my daughter's wedding. Most convictions are conditional, and some are VERY conditional. It's also possible I don't drink because I'm a recovering alcoholic. If you see me with a beer it doesn't mean I'm a hypocrite, it just means I'm less than perfect. Convictions are also very temporal, and it only takes a moment to succumb to temptation.
You certainly shouldn't judge a man based solely on what he says about himself, but I think it's almost as dangerous to judge based only on incidents taken out of context. The smart man, I think, judges patterns, repetitions, and context. The wise one, of course, doesn't judge at all.