1)Tell me something about yourself and something you are proud of. To me this is the same question as – sell me this pencil, only the focus is on a product he should know very well, himself. Listen to the answer, the actual content is not as important as the attitude, demeanor and self confidence.
2) What do you know about us? A big part of sales is pre sales preparation. Fail to Prepare: Prepare to Fail, as the saying goes. See how prepared the prospect is for this interview. A well prepared prospect for the interview, will be a well prepared sales rep for your company.
3) Tell me about your hobbies. Look for a team player. Someone who has a past in sports or similar activity will appreciate the value of individual skills in a team environment and knows what it takes to win.
4) Tell them you are looking for a top performer and suggest that they don't seem to fit the bill. Sales reps need to know how to handle rejection. See how they handle this negative response. If they will fight for themselves in the interview, they will fight for your product in the field.
5) Do you have anything else to add? A strong candidate will summarize, get agreement and ask for the job.