As a student I worked in retail. I was expected to invite conversation with open questions. It’s harder that it sounds. Years later when being trained in user research I was encouraged to ask why. Not only why, but as many whys as I could … and you know why … to get to the root cause, that deep fundamental driver of behaviour. Of course this too is not as easy as it sounds. Unless you’re a charming 5 year old asking why can sound pretty obnoxious and being asked why can make anyone feel quite defensive. I’m guessing advice like this has its roots in the famous 5 Whys, which I take to be a tool of analysis, not a script. If you disagree with anything here, or have more to add please say so in the comments.
And if you are looking for more in depth information on conversation for design research read Ethnography for Marketers.