Personally, neither me, nor my managers care whether the applicant is clean-shaven or not. What matters is that you look neat in appearance. I have a goatee and my director has a beard.
When it comes to clothing, I would AT LEAST wear a dress shirt and pants, that are clean and wrinkle free. First impressions make a difference. Also, just becaust the employees are casually dressed, doesn't mean that you can dress the same. You don't have the job yet, they do.
Along with retail experience, they are probably looking for someone with a good, outgoing personality, who's going to be able to fit in with the other people.
When i'm looking to fill a position, I look for personality first, then experience. I can teach you whatever you need to learn about your job, but, I can't teach you how to have a good personality.