What's your experience with getting participants to speak to you for win/loss interviews?

I have found that customers are more willing to share their experiences in win-loss interviews than you might think. The keys are to:

• Make it clear that you're not going to sell them. Make sure that the outreach doesn't sound like another outbound email. 
• Position yourself as neutrally as possible. The purpose is to help improve the product, more than improving marketing or sales. (That information will come anyway if you ask the right questions.) 
• Respect their time. Ask for 20-30 minutes (depending on the nature of the sale and your audience) and stick to it. Be prepared with the right questions and background information from your CRM. 
• Have a few open-ended questions ready. I have gotten some surprising answers in win-loss interviews.