Absolutely agree here. Something like 80% of how we communicate is not in spoken word, it is tone of voice, facial expressions and body movement.
Make sure to ask broad questions and ask why a lot. If you get awkward silence you are normally on the right track. Be patient and wait out the silence, people love talking about themselves.
Pro tip, keep asking why until you get to emotional needs. Let's say you strike on a pain point, don't stop there, so what if it means that it takes twice as long to enter an order. Why does it matter that it takes so long? What would they rather be doing? Why? Does it mean that they can't go home early and pick the kids up from school? Does it mean that the boss will think that they are slow? Does it mean that as a business owner they can't spend their time on more important things?
The more you understand and build empathy with your people, the more you understand the problems they have and the more likely you are to come up with the best solution.
The user observation tool at http://www.black.design/ might help you organize a session.