When Benjamin Franklin wanted someone to like him, he'd ask that person to do him a favor, because he noticed that people who'd done him a nice turn would rationalize this by assuming that they'd done so because they liked him, and so they'd continue to do him other favors in the future based on that affection.
At The Jerx, Andy describes how this principle can be used in person-to-person amateur magic effects: by asking the person you're performing for to help you do something that seems integral to the trick (whether or not it really is), you're getting them to buy into it. He suggests kicking off the buy-in by asking the person you're performing for to be "all in," and continuing, "If you're in though, I want you to be all the way in. Be here, and try and be open to something happening that is a million miles from normal life. I have a plan of action, and I will steer this ship. Are you in?"
Much of this is reminiscent of a con job (as is often the case with magic!), but the point here isn't to trick the person out of something, but rather to give them an intense experience of something magical happening, while they willingly suspend their disbelief.
A few weeks later he did just that. He was out at a bar talking with a couple friends and asked them if they would be willing to come along with him to see something a little freaky he had discovered at the old nuclear power plant. "It might be a little weird. I don't think it's dangerous, really. But I only want you to come if you're 100% onboard." Who could resist that invitation? So they drove 20 minutes out to the plant, got out and walked about a third of a mile in the snow around the fence until they got to the "right spot."
"Do you feel it?" he asked.
Standing outside in the winter in a deserted area by an old nuclear power plant you're bound to feel something. "Here…uhm…let's see… oh, give me your ring." He takes the borrowed ring places it on the palm of his hand, waits a good long while, until eventually, by the light of the moon and a cell phone, the ring flips up on its end, raises in the air and floats to the other hand. Mayhem.
They know he does magic. They know, on some level, it's a trick. But it's also something more because they've invested more in it than they would in "a trick."
(Image: Chapeauclaque, Peng, CC-BY-SA)