Fun part was, I could gauge exactly what kind of customer they were going to be like as a function of how they reacted. If they were really amused and cool with it, they were going to be a good customer. If they were a little pissy about it, they werent going to be a lot of fun. Anyone who was mad but jumped at the free lunch...a cheapo.
Makes sense, you're surprising someone with an unusual but actually beneficial situation/proposition. The root of it is you're fulfilling their wish for a free lunch, just not in the way they anticipated. Their reaction to that situation can be very telling...
Since these were also business lunches, I also got to eat a lot of those hideously expensive burgers for free. And my boss (who worked out of another state) thought I was quite godlike in my ability to line up a new prospective customer for lunch almost every day.