I coached a manager who'd hired seven people in the previous year–and had fired five of them. His manager was ready to toss him out, too. Instead, the senior manager decided this manager needed coaching about how to hire people.
When I asked the manager about his interviewing style, he explained that he used what I call irrelevant and hypothetical questions. (In the links, I suggest ways to use those questions. This manager was not a savvy interviewer.) In addition, he made all the decisions about hiring himself.For this strategy, review and possibly update your job analysis. Develop at least two behavior description questions for each quality, preference, non-technical skills, and technical skill. Develop some auditions. And, practice your interviewing with someone else, someone who will give you feedback. Finally, use your interviewing team to help make the hiring decisions.
When people aren't working out, too often the problem is the hiring, not the person. It's possible to make great hiring decisions. It does require some up-front work and practice–especially of learning how to interview successfully.