Opti Staffing interview questions

The recruiter asked a few questions about my personality and strengths, This was a good experience but just curious why the company wanted me to sign a few government documents like I-9 or W4 before being hired Is that a normal process?

The interview process was a simple one being that of the office manager and upper management. It was simple and I knew what to expect. There were no issues. Both were virtual interviews, but it was also during the pandemic .