Medical billers perform a variety of tasks depending on the employer and/or exact position.
My personal opinion is if you are comfortable with computers, you can learn 95% of a new system in a few days. It shouldn't be a requirement for an employee you are looking to hire for a long term position. If you are working contract jobs that might be very short positions, then I could understand requiring experience with the specific system(s). Again, just my 2 cents, but there are far too many computer systems out there for people to know all of them. Knowing Epic is not going to help if the system is Allscripts. And in large healthcare systems like mine, we use MULTIPLE systems every day (1 for scheduling, 1 for outpatient records, 1 for hospital records, 1 for insurance verification, 1 for profee A/R, 1 for facility A/R). If I was only willing to consider candidates with experience on these, even I wouldn't be working here.
Whenever I hire (for any position - biller, coder, front desk, surgical scheduler, sonogram tech), I could not care less if they know my computer system(s). I hire for whether they have the basic skills/certification/understanding of what I am hiring them for, and what I'll call "fit for the position." I always want someone open to new ideas, willing to learn and a team player. Someone sharp with a good attitude. When it's a more senior position, I also want some problem solving skills. And your resume needs to be a good enough match for me to even set up an interview.
What I look for in my front desk staff is not the same as what I look for in my coder. My front desk staff need to be friendly, cheerful and more outgoing. If I am hiring a remote coder with zero patient interaction, it doesn't matter too much if they are cheerful or not. But my remote coder better know how/when/why to properly use a modifier.
I also appreciate someone willing to work their way up into a more complex position if their current experience is significantly less than their education/certification. For example, a CPC-A willing to take a billing position and learn the systems/practice. It's a chance for them to utilize at least some of their coding knowledge and demonstrate to me why I should move them into a coding position that might typically require coding experience they are lacking.
To me, "medical billing" often means claim follow up, and the primary skills for that are persistence and organization.
I realize not all hiring managers have the same approach as me. There are many organizations where the person interviewing doesn't understand the skills required of someone in the position. If the job description is vague, ask more details about what you would be doing day to day. Is it 10% patient interaction, or 90% patient interaction? My best advice regardless of position is to be professional, open and confident (but not arrogant).