Gaining access to respondents and reluctance amongst respondents are the biggest problems faced by interviewers in terms of conducting the interview itself. There are many reasons why a respondent may be reluctant to be interviewed, either generally or in relation to a particular question. Adler and Adler (2002) suggest that unwilling or reluctant respondents are spread throughout society. They tend to fall into groups: secretive respondents (those with secrets who fear being found out), sensitive respondents (sensitive about personal matters such as financial matters, health and disease or sexual conduct), the advantaged (those in positions of wealth, status or power) and the disadvantaged (respondents may be at risk, may be engaged in criminal activity, or distrustful of the intentions of the interviewer).
Incentives such as money or gifts are often used to encourage respondents. This however, is a controversial subject amongst researchers, some believing that pay offs may provide access to respondents but do not necessarily build trusting relationships or guarantee good quality results.
It is important to remember that the vast majority of respondents will be willing to be interviewed but reluctance amongst respondents is something that you should consider when designing questions and selecting your population sample.