The interview process is one call to let you know you need to come in for a in person interview after you put in your application (can take weeks before they call and it has to be in a season they are hiring or if they have hiring now signs)
They will have you go into the backroom, which is usually very full of boxes and games and controllers all over the walls and sit you down to talk to you. My GameStop had a working T.V. and a PS3 hooked up in the back to play games and watch HULU.
The assistant manager (in most cases) will ask you some standard questions, like "what made you want to work for GameStop", what do you know about GameStop? And of course "Why Should we hire you over someone else?"
basically, as long as you have some knowledge in a area not on PC, like Nintendo, or PlayStation, you will be doing fine. If you tell them at any point you are unable to do sales of any sort, you lost your interview and they will move on to someone else.
Try being honest, as this is a small company, there is only gonna be at most like 10 of you all together on the schedule, if you believe you are willing to learn and understand more than you know already, let them know. Share that you want to know feedback for what you are doing wrong and if you can ask questions to improve your sales, I personally was not good at sales before, but I think with those already settup, my managers were more willing to swoop in and help and guide me than if I didn't mention I wanted to learn more.