Begin the answer with "I would need to know a little more about your day to day. Would you mind if I ask you a few questions first?" And move on to questions such as "What is important to you when selecting a pen?" "What do you usually write with?", etc.

For more seasoned sales professionals, the interviewer may skip the fun and games with the pen and jump straight to asking you how you would approach selling the company's products or services. Do your pre-interview homework so that you'll be able to speak intelligently about the products/services and their benefits.