As a customer, I find that fashion photos with models either smiling or dancing or whatever make them look like they are having fun, make people want to buy the clothes more, compared to photos that models look cold, serious or something like that. I can't deny that photos with models looking cold are very beautiful, but somehow "happy" photos just make me feel happy too and want to buy the clothes. Maybe by seeing "happy" photos, customers are told "Buy these clothes, you will be happy like us!" without knowing it.
