What’s the Right Kind of Bonus to Motivate Your Sales Force?

Companies typically compensate their sales force by using some combination of salary, commission, and bonuses, but executives are often unsure of which incentives provide the best motivation. For example, should bonuses be tied to quotas or should they be given unconditionally? For a quota system, would it be better to use bonuses as a reward (giving them to those who meet or surpass their quotas) or as punishment (taking them away from those who fail to meet their quotas)?