Boy, that's a toughie, isn't it? It would be really easy to stammer through a stupid answer in an interview. What they are really asking you is "Why is it in our best interest to have you working for us?" So tell them. An interview is no place to be shy. Tell them How you will be an asset to the salon.

E.G. Because I have a strong work ethic, I'm great at time management, I understand the importance of superior customer service and I am willing to do everything I can to help the salon and myself grow.