If you are planning to work with the customer for a long period, please read about their vision and mission. You want to align your projects according to what the customer wants.
Ask good questions. Read The Mom Test. Here's a summary: https://www.slideshare.net/xamde/summary-of-the-mom-test
Some people are more comfortable communicating in text, and removing the interviewer can lead to more honest responses (by virtue of eliminating interviewer bias).