Eileen,
It's true, students sometimes feel more at ease with a guest speaker, asking probing questions about the work setting, wages, work conditions, advancement, and so on. I think because the speaker is an outsider students may feel more comfortable asking "insider" questions. And usually, the guest speaker is willing to share information without hesitation. A good guest speaker can reinforce the students choice to attend school, perhaps in part by answering these types of questions.
Barry Westling