We learn early on from this exchange between William McIntyre and the man in black that this game isn't going to be fair. They're pulling the strings from behind the scenes.
"The Cahills have had a greater impact on human civilization than any other family in history." (2.104)
Manipulation comes pretty easy to a family that's been doing it for centuries. The Cahills might as well be the Illuminati. But easier to pronounce.
"Most of you, I'm afraid, will decline the challenge and run away with your tails between your legs." (2.106)
Grace's taunting here is a subtle manipulation of her family. It's like she's saying, "If you don't participate in this game, you're a coward." That might convince some people do it. And she can't exactly force them any other way, being dead and all. Manipulation's the only option here.
"I'll put [your inheritance] in an account for you until you're adults. I'll only spend the interest." (3.46)
Aunt Beatrice is pretty slick here. She's using what people in business call the "assumptive close," fully believing Amy and Dan will just agree to letting her take their two-million dollar inheritance. Thankfully they can't be manipulated that easily.
"This family has been instrumental in shaping human civilization. Some of the most important figures in history have in fact been Cahills." (3.58)
Because of this, it's not that surprising that the Cahills involved in the clue hunt are the manipulative masters they are. This family has been doing it for who knows how long. The world is just their toy to play with.
Grace had insisted on renewing [their passports] last year. (6.82)
By doing this, Grace was making sure that Amy and Dan would be able to participate in the contest without even telling them about the contest. That's pretty sneaky.
"Does it seem odd to you that we happened to find Irina Spasky out of ten million people in Paris?" (12.3)
Amy and Dan come from a family of manipulators. They should take an extra three seconds to think about how conspicuous Irina—a former KGB agent—is at this moment and realize it's a trap. Then again, Amy and Dan are 14- and 11-years old, so it doesn't take too much to pull one over on them.
Despite all the security, it still seemed like they'd gotten in and out pretty easily, and [Amy] wasn't sure why. (14.10)
Poor Amy and Dan are a little slow on the uptake. To be fair, they're just kids. But they're smart kids, and they're aware something strange is going on. Why don't they smarten up and stop falling into traps? Are you screaming at your book at this point?
"Maybe you'd like to know about the night [your parents] died?" (15.121)
This is some hardcore manipulation on the part of Uncle Alistair. He's trying to get Amy and Dan to do what he wants by telling them secrets about their parents' deaths. In case you weren't certain that he's a total jerk, this proves it. The only way he could go any lower would be if he killed them himself. Then again, we wouldn't put that past him.
William McIntyre took out his cell phone. He showed his colleague the screen—the last number he had dialed in Vienna, Austria. (20.8)
The manipulation doesn't end with The Maze of Bones. This foreshadowing in the last chapter shows us that Mr. McIntyre plans on being a puppet master along every step of the hunt.