Determine training needs. Separate the successful from the less successful. Measure their own sales managers. I don't want to stop there, however, because many stores in this industry are in fact measuring their sales people in one way or another. Unfortunately, the vast majority of these retailers use ineffective methods.
Many retailers judge sales performance based on individual sales volume.
They track this figure over time and post the results in the lunch room. Most see this as a form of motivation. After hundreds of interviews with sales people, however, I can tell you that this, in their minds, is a subtle form of punishment. The people at the bottom of the list feel less motivated because their poor performance is now public knowledge. Measurement should never be used to inflict punishment, whether intentional or unknowingly.