It’s on both of you. The employer’s HR department needs to have some sense of what constitutes a reasonable offer so they aren’t a) overspending, or b) wasting everyone’s time by lowballing applicants. It’s on you to research Bureau of Labor Statistics data, Coroflot salary survey, Salary.com, and Glassdoor data to establish what you can reasonably ask for based on the job title, your experience level, the the employer organization’s characteristics, and the location of the job.