my employer employs the system of monthly evaluation by name variable incentive. the scheme pays part of your package depending on your, your dept and your companies sale performance. so if your sales people are not working then you lose your earning no matter even if you are a peon or a clerk. further you will lose it if you leave the firm during the year. these acts as a disincentive to hard workers and infact drives out the initiative out of you.
and these things are never clarified while giving you the appointment letter. it is always a win win situation for the employers.