How does a celebrity's smile affect his personal brand?

My questions are about “The impact of a celebrity’s 'SMILE' over his personal brand”.

1. What impact does it have on the minds of the people that the celebrity wants to attract, e.g. in case of any product endorsements, he has to attract the customers for the product he endorses?

2. But if he is not endorsing a product, does he still have to keep a positive and upbeat image about himself in the industry? And if so, does his smile help him in that?

I'm therefore looking for answers to the following questions:
- In what way does a smile influence (the observer’s) behaviour or perception?
- If it influences, how is it reflected over the personal brand of the celebrity? If it shows a favourable image of the celebrity, what happens when a celebrity performs badly, and would the previous likeability of the celebrity diminish, i.e. does his personal brand’s ranking decline?

In short, does the personal brand of a celebrity depend upon his personal performance out there in his skilled area or upon his popularity with the public?

In all the above questions I am assuming that the celebrity is very visible to the public, appearing in the media often, like George Bush and Manmohan Singh (PM of India). Although the questions seem to be hypothetical, I'd like ideas and comments about them, especially from specialists and professionals participating in this marvellous service.

Thanks a lot for taking the time to read and anwer my questions.