Emphasize the importance of great customer service and be ready to discuss what great customer service means to you. Tell us about a time you received horrible and excellent customer service, what was each experience like? You may be asked to sell something random in the interview--e.g., sell me this pen--you will need to discuss the reasons to buy the pen (you have expressed to me that you need a pen...this is a pen. This pen is superior to other pens because it has black ink, a smooth writing ball point, and a click top closure function that eliminates the need for a pesky, and often lost, pen cap. This pen is also on sale today only when you join our store membership program etc etc etc). You come in talking customer service and ready to sell...good luck not getting a job at this lovely company!
Working on the floor is obviously very customer focused, but there is always restocking that needs to be done. There is always something that needs to be done, and there is little time for conversing with coworkers. Most importantly, chatting can never never interfere with customer service. You do not want to get a reputation for chatting with coworkers.