Most people realize the interviewing stage is the last time you'll probably have influence on the amount of your salary. Once hired, your salary is dictated by policy coupled with company and individual performance.
Although this is a common fact, many job seekers lose sight of this during the critical stages of landing the job. They later find out they are paid less than colleagues in similar positions. The key to avoiding this fate is to be armed with information and be able to sell the value you bring.