How do you justify your salary?

Salaries should be based upon work experience and education. There are times, in certain professions, when time spent "on the job" is the same as having an educational degree. You can't "learn" or "get" work experience from a book. Also seniority in a job position has merits for salary earnings. Longer term employees will tend to have higher salary rates as opposed to new hires just starting out in a profession.