We feel that you may not have what we are looking for. What would you say?

In this case the interviewer may have a number of objectives. It may be intentional to put you under pressure and see how you behave. It could also be a test to ascertain how well you understand their requirements and how well you believe you match them. The answer again lies in the common points that may be in the job specification or job description and your CV. Remember that what has got you to the interview is the information in your CV. You should be able to very simply highlight your most relevant achievements using the skills and attributes they are looking for and use this to underpin your credibility as someone who fits the job.