I like the way this fellow approaches performing a customer interview.
He urges you to start with soft questions: "However, I found it far more effective to ask basic (but useful) questions up front. “What’s your role?” “What was the process you went through to purchase product X?”" This builds trust and sets the interviewee at ease.
And to ask customers to tell stories about their experiences: "It’s easy to for people to spout their opinions. Stories, however, are more useful for making sense of difficult situations". I think this technique helps avoid customers sugar coating what goes on.
He also provides some good reference links as well. Plus, he likes the way Terry Gross does an interview (as do I!)
Read the real thing here: http://caddellinsightgroup.com/blog2/2009/05/the-art-of-the-customer-interview/