My first real job was at CompUSA. And my experience was identical to what you just described.
I was just a high school kid stocking shelves, but knew as much or more about the computers as the fulltime commissioned sales people. I was constantly getting paged to assist a salesperson.
I would do all the work, explaining the product and helping the customer make a decision, and then the salesperson, would say "Thanks, I'll take it from here."
Also, their theft control was atrocious. The cameras were not on, the guy checking receipts at the door barely looked, and people just walked about with expensive stuff all the time.
Wasn't surprised when they folded.