I had been referred for a position and the interviewing official knew that the client would accept me as an on-site employee (the client knew my work already) , so the interview was fairly basic. My sense, from my interview and those of others I've spoken with, is that NG just wants to put people in client seats and doesn't try hard to really get at someone's real level of expertise or their ability to work with others. The most important thing is to show that you, as the interviewee, know what the client needs and that you're interested in providing it to them, not causing any headaches for NG. So, research the client!