The biggest rookie mistake when interviewing customers is asking them what they want. Never ask them what they want. Rather, introduce them to the platform, explain the benefit of using it, and then let them have a trial run.
After some initial testing, ask key usability questions, like what things they would improve, change, or would like to see that isn’t currently offered. Ask if they ran into any snags while getting a trial run and identify troublesome areas.
And of course, remember to smile and thank them for their time!