People are generally predictable. We follow patterns and programming within us. Most people will simply follow the crowd, this is called the "Herd Instinct."
It's also the reason a "Pitchman" will call a couple people in and ask them to hang around while he does his pitch. Of course others in the "Herd" see these people watching and follow suit, either wondering what's so interesting, or just doing what they see others doing, that's human nature, and so a crowd gathers. A crowd always starts with one or two people.
I have my own way of looking at things and breaking them down, I put the majority of people in three catagories. "Leaders" "Followers" and "Followers that think they're leaders"
"Followers that think they're leaders" seem to be the easiest to manipulate in my opinion. All you have to do is pretend to follow them, acknowledge their leadership, and then make subtle suggestions in a way that they think it was their idea, then back them up on that idea and they will follow through on it.
"Followers" on the other hand need to be lead directly, they will always gravitate to the strongest person. You must be blunt and to the point with them, you must "tell" them, not "suggest". Also, you must be unwavering, confident, if you waver, they will follow someone else.
"Leaders" cannot be lead, that's why they're leaders, but they can be persuaded. It must be put forth as a collaberative effort though, or they won't do it, "leaders" collaberate, they don't follow.
Again, confidence is important, one cannot waver, you must be straight and to the point, and strong.
These are things I've learned about human nature on the road, working with the public, and working with Carnies on a crew.
Midways are set up in such a way as to direct the "Herd". It works the same way with Casinios. The Midway is setup so that the public will move in a certain manner and direction.
People can be predictable at a personal level too. I liken it to predicting the weather though, you can learn to give an accurate forcast but unforseen circumstances can change certain variables and throw things off.
I learned a lot over the years from the old guys, some Game Agents, some Pitchmen, and a couple Sideshow people.