People usually take perception for granted and trust it completely which can sometimes result in some sort of illusion. Take for instance the trick Derren Brown is playing of these people getting them to allow him to pay them in paper. It is amazing what someone can do with the knowledge of how to alter one's perception into thinking situations such as allowing someone to pay you 4,500 dollars for a ring in paper is ok. In order to achieve this illusion Derren Brown tells the sales person the line, "take it, it's fine" as he is handing him the paper as a payment for the item he is purchasing. The illusion is the perception the sales person is receiving from Derren Brown that the paper for the moment he is telling him, "take it, it's fine" is a perfectly acceptable payment for the item he is purchasing.
The book talks about how some "illusions can illustrate principles of sensation and perception." p.145 That is exactly what Derren Brown is doing to create this illusion. He is correlating a sensation by telling the person "it's fine" they are going to naturally feel more of a sense of calm and gratitude, by putting the paper into the person's hands they are also feeling the sensation of receiving something in return for what they have given him. In other words a payment. By putting together the phrases, "take it, it's fine", he is allowing the person to perceive that the sensations he is feeling are good and that they should feel at ease with the situation.
It is interesting how easily Derren Brown was able to deceive these people into taking the paper as payment by merely telling them, "take it, it's fine". It shows how easily someone's perception can be altered to create an illusion such as paper becoming money. This reminds me of the ways many large retail stores use their advertisements to give consumers a false perception of what the store is really selling and/or how much they are selling it for. An example would be a Big Mac from McDonalds. On commercials they show the viewer pictures of a delicious, juicy looking burger in a warm, soft golden brown bun with crispy bright green lettuce and red tomatoes bulging out of the sides. When you go there and purchase one the experience is not at all the same. When receiving the burger it is all squished and wrapped up in a crinkled paper. The bun is completely smashed, the hamburger itself incredibly greasy and the lettuce and tomatoes are scarcely there. This is a common illusionary perception that affects people every day. Therefore these types of illusions have replicability.