Based on the interview I experienced, I would do your best to really look at the clothes in the store. If you want to do this early and research online, that's an option, but being at the store right before the interview and looking around (which first off, looks super involved to the manager) really makes a difference as opposed to online. Really look at the clothes, get a feel for the style and the type of market/people they are trying to sell to.
The interview itself asked questions like :
How do you deal with difficult customers?
How do you deal with a stressful situation?
Sell me this pen
While the first three questions are ones that one can generally figure out an answer to, the last one really caught me off guard. While every person sells an item differently, I think the best thing to do is to smile and just point out good qualities of an item. I realized after the interview that I didn't need to exaggerate or make it sound really fancy. I just had to point out things like "the pen writes in black ink, making it more universal than pens that might be blue or red. The pen also has a nice cushion grip so your hand wouldn't get sore while you write". If you point out the simple qualities, people can relate to that more. Besides that, dress nicely and smile!