The person either has a strong emotional dislike for agencies or her/his hands are tied by the boss or the 'evil' Personnel Department. In either case this is a strong feeling!
“I understand how you feel.” MEAN IT. “You don't know me, but there has to be some good recruiters that can really add value; otherwise, they would not exist, don't you agree?” “What can I do to try and prove that I could just possibly be one of those people that can add value, without taking too much of your time?” Another good approach is getting them to talk about a bad experience. Ask them to tell you about their negative experience and turn this into an opportunity to give you a chance. “Are you aware of the difference between an Agency and a Search Firm?” Explain that, unlike agencies, you screen both your clients and applicants heavily. You search for the most qualified candidate for each position you are given. Or simply ask, “What happened?”
Another question which would provide useful information is, “What can the recruiting profession do to improve our service?”