My interviews were usually performed by two people; a CEO and one board member when I worked for corporations. I also worked for a sole proprietor who owned several businesses, and after a couple of years with him, I asked if I could put him on a fee basis so I could do consulting work. I computerized his business, and established a standard cost system for his stores. I also advised him to develop a large property he owned in Cupertino, and now leases his building to Apple Computer. He said okay, and my income bloomed dramatically after that. I bought income property, and partnered with several other people to buy a condo at Incline Village at Lake Tahoe.
When I worked in management, we let managers interview their own prospective employees, but when we interviewed for management positions, several managers participated in the interviews. I also taught managers interviewing techniques that I learned by attending a seminar. Also taught managers how to process performance evaluations. Most managers hated to give their workers poor evals.