It is. You can basically check out the company linkedin, people in similar roles/YoE, then google their name to find out their birthday, then just call our IRS. Ask for declared income for year X, X-1 etc. This gives you an anchor as parent said. It's a way to change the power imbalance when negotiating. I know friends that do this when applying for jobs. There's a law coming that makes this basically worthless, since the salary range for the role must be declared openly with the ad. And that btw is one of the first questions I ask when talking to hiring manager or HR, to find out if it's a good fit.