Customer isn't always right, but they still decide what they value. In other words, you should consider your understanding of customers' needs and what they value as assumptions that need to be continuously tested.
I've written before how to do customer interviews and go beyond them. Simply put, customer development is process for building new corporate ventures and startups. It complements your product and business development activities.
One of its core tenets is to get out of the building, and face the real world. What does that mean in practice?
No need to overcomplicate it. Make sure to repeatedly visit everyone connected with your product and/or service: customers, customer's customers, suppliers and vendors, market and subject matter experts, and other relevant ecosystem players.
Don't turn this into a project you do once a quarter or annually. On the contrary, this should become an organic activity; part of your daily and weekly schedule. Minuscule investment for a wealth of insight, which in turn will help you create more value.