Poor neighborhoods, especially urban ones, get pretty familiar with scams and money games. This is that "cultural inheritance" the authors are talking about.

This is not a zero-sum game for the neighborhood. So if you don't conduct the study quickly, you risk the participants identifying each other and agreeing to collaborate to extract the maximum possible gain from the outsider.

On the other hand, if you plan to show up and run the game quickly, you'll need to have a lot of cash on hand to pay out. (You are paying out on-the-spot, aren't you?) You're going to risk drawing a crowd. The police will likely take an interest in what's drawing the crowd and this scheme will look a whole lot like gambling.