This is a great point. There are absolutely candidates who are "good interviewers."

I think one of the most helpful methods of determining a good interviewer vs. a good future employee is taking a structured, situational interview question, i.e. "How would you go about selling a new product to a customer?" and turning it into an actionable work sample that is tailored to your company. "We make this piece of software that does this. Spend the next 10 minutes writing a cold email to a prospect that outlines our offering." As the interviewer, grade the work sample on structured criteria that is important.