As a sales person what do you do if you feel stuck at sales interview?

Normally, I would consider that a sales person would have done his homework before appearing for sales interview. He would have considered & examined all skills he is presenting with and gaps between his next jump for new job opportunity and his current standing.

If at all he is stuck I think it will be fair to humbly accept that he does not have answer for the question asked, this will prove his transparent and trustworthy approach to the interviewer.