A fixed salary does not vary from month to month, whereas, a salary based on incentives may vary as it depends on the performance of an employee. 
Salary based on incentives is the best in the sales industry rather than a fixed one. It motivates the employees to achieve their goals. The technique of convincing and persuading a customer varies from one sales person to another. So, the salary is paid according to the performance of an employee.   _{Your Comment}