Co through the Questions in the Questionnaire

Based on your test plan's user profile and the questions for the screener, question the person about his or her qualifications, such computer experience, job responsibilities, and equipment used.
■ NOTE if you are using an outside agency, have the agency first try the questionnaire on you as if you were a potential participant See how the person who calls you responds to different and/or ambiguous answers to the same question. It is your money and your study. Make sure that the agency does it right.
If possible, use the questionnaire as a checklist for managing a more conversational interview, turning the questions into open-ended queries so as to get the respondents to volunteer information about themselves. This way, the respondent is less likely to be able to guess the "right" answers to get into the test, and you may learn additional things that could be useful to know.