Commission Pay Structures

I am an employer and am about to negotiate a salary / remuneration package with a new employee. The position involves managing a small business (in the education field) with a significant amount of sales work required and various KPIs to fulfill. In principle, i am a big believer in performance-based pay as i think employees should be rewarded for good work. My question is how to structure something that will effectively reward the manager for good performance.

I am thinking along the lines of a relatively low base salary + percentage of monthly turnover / profit. A few people i have spoken with have suggested commission based salary packages don't work that well. Any ideas??