If you're given the opportunity to speak or answer a question, speak with enthusiasm. Ramble a bit if you need to. Don't speak with a monotone, and don't speak softly/quietly.
With most jobs, they won't hire anyone they don't like, so you need to be the most liked. This is probably most true in the retail sector. If they don't like you, customers may not like you.
With this particular job, they probably won't hire someone who doesn't seem easy for people to talk to immediately (i.e. within the first 5 seconds of talking to you), or isn't able to speak with enthusiasm about their products.
I know you are excited about Apple products, but you need to project it. Project project project. Nobody gives a crap if you can answer the question. There are 20-25 other applicants, and 10 of them can probably answer the questions just as well as you can. Heck, 2-3 of them may be members of MacRumors. 😀 While your goal should be to answer the questions to the best of your ability, your primary goal should be to leave an impression. Be remembered. Otherwise, you'll just be remembered as, "The guy who was sitting near the window."
