Imagine this: you are visiting from interstate on other matters. Your “colleagues” (you have never met these people but it could be said that you share similar professional interests) hear of your visit and invite you to give up your time for free to present a breakfast talk to a closed meeting at their place of work. They say they have a “poor understanding” of your area of work and would like to learn more. Can you help them out?
You think this is a reasonable and a not uncommon situation, so you agree. You get up early, give what you think is an interesting presentation, engage in an active Q&A session, get thanked by the organiser for making the effort and contributing your time and goodwill to foster greater understanding and intellectual debate within their department. You think that is that.