If you enter a salary discussion without researching, you put yourself at a disadvantage. A hiring manager has no obligation to make you a competitive offer. Thorough research helps you recognize when a salary offer is below market value.
If the salary is firm, you can negotiate additional benefits or perks. The company may view benefits as a less costly way of keeping employees happy.
Some cities and states have banned employers from asking questions about salary history, but it could come up. Avoid disclosing your salary history if asked about it during an interview.
Negotiating your salary after receiving an offer is generally better than during the interview process. Playing hardball during the early stages of the hiring process could eliminate you from consideration.