Professionalism in customer service implies that you are ready to take responsibility for the experience you are providing your customers. This means that you, as a front-line company representative, care about the amount of time your customers have, you care about their feelings, and you are sincerely interested in performing your job professionally and serving your customers right. All customers deserve your full attention and a polite, friendly attitude. That's the simplest way to show that you really care and helps you foster a wholesome experience that will last.
Lastly, always put yourself in the shoes of the customer. How would you feel, what would you think, and always think of how you look from a customer's perspective.