I used to work there and they DO NOT get commission. Sales are tracked per sales person however, and it's a measure of performance (as it would be for any workplace). So if you want to move up, you've got to be a decent sales person. Again, like at any workplace.
Personally I never found it too hard. You just be nice to the customer, make them feel comfortable, try to figure out what they want, and do what you can to help them find it. Offering commission would impede that.