Let's face it: being shy and customer service do not make a very nice mix. Being outgoing can keep any situation positive, fun, and light. While interacting with customers, being outgoing puts them at ease and makes them feel like they are being helped by a friend/family member, instead of a salesman.
In my current role, I am outgoing both on and off the sales floor. I am a huge believer in staying true to yourself without trying to be someone that you're not, and people will read that and appreciate it more than anything. When they do, it speaks volumes about the type of inviting personality that comes along with it.