Sales Executive Import Question:

You risk coming off sounding conceited or being cross questioned if you answer this one too early. Instead consider the following answers as possibilities.
"I don't yet have enough information about the position and your company, to tell you that I can do this job."
Continuation 1: "Since you've invited me to this interview, could you please tell me what you see in my qualifications and experience that make you believe I can do this job?" (I'm not looking for assurance from them; I answer and ask with confidence in order to obtain information) If the interviewer does not have a copy of my resume present, I will instead ask if he or she has had the opportunity to review my resume.
Continuation 2: "Would you mind if I asked a few questions I've prepared to get to better understand the job first?" The employer would be unreasonable to say "no", and you can come back to answer their question later once you know more about the position.