ask the tester to take 20-30 minutes to test the product. At the beginning of the audition, I hand the tester a few blank defect reports. As the tester tests, the tester write defect reports as the tester finds problems. At the end of the audition, I review the defect reports with the tester to make sure I understand what the tester meant in the reports. Then I evaluate the defect reports after the tester has moved onto the next interview slot.
In addition, when I'm interviewing someone who hasn't tested a product in our product domain, I'll ask questions about the candidate's ability to learn quickly, such as: "Tell me about a time you joined a project where you didn't know the people or the product. What did you do?" If a candidate hasn't had to learn quickly, you don't know if the candidate will be adroit enough to pick-up necessary skills. If the candidate has been able to learn quickly in a different situation, judge if the situation is similar enough to your project. Then determine if the candidate can adapt to your project.
These behavior-description questions and audition will help you detect if a tester is right for your project--regardless of whether the tester has previously worked on a similar project or not.
If you can't wait for or afford the perfect candidate, look for analogous experience and the ability to climb learning curves. Make sure you ask about specific aspects of previous projects that help you determine how the candidate performed relevant work.
Take the risk out of hiring. Incorporating tests and auditions into your interviewing process will help you build better teams.