go stand and watch in a store that uses commission to motivate staff...Good god no, why would you want that? Then employees are constantly trying to "one up" sales. As an example, if an Air is perfect for customer X then the employee is wasting time trying to pressure the customer into a Pro for the commission. Furthermore, just like in car sales, the concept of being "up" will creep into the culture as employees jockey for opportunities. They might also judge customers and bypass accessory folks looking for those that "appear" to be looking for systems.
I believe that Apple retail employees are regarded as having a pretty good package already compared to other retail positions. I would argue that a slow week of customers can cut into your pay while luck of the draw benefitted a coworker. In theory it all averages out but I prefer a base/bonus plan over base commission. Bonuses can be paid based on overall store performance or an employees rating with customers, etc.
I agree 100% and never have been a fan of the commission structure for the reasons listed above. What you could do is offer something for add-on sales like AC+ or cases, etc. The kinds of things that savvy shoppers buy outside of the Apple store as not to pay the "Apple Tax" on expensive accessories.
i watched a salesman upsell to some old people a computer that was well over specced for what they told him they needed. same guys also managed give $50 off a $3000 tv to another older couple. if they'd done their homework, a before the price was a $1000 less. I know it's buyer beware, but commission sales people are motivated to maximize their income not your needs.