As with any retail job, it is paramount to sell your people skills. You'll need to be willing and open to making quick contact with anyone and everyone who walks in the door. It is not simply enough to be a register operator. You must know how to ascertain what a customer wants and what they don't know that they want ("upsell"/"filling the basket"). What other games might they be interested in? Do they need additional accessories or guides?
That said, when you're actually working, many people don't enjoy having those "skills" used on them. But you asked about how to get the job, right?