Here's a little practical evil for the holidays. Does someone want something expensive? Get them the cheap version, and then use choice blindness to convince them that they like it.
Choice blindness has been featured before on io9, but usually in the context of how little human beings really care about each other. A group of male students were asked to look at photos of young women, and choose which woman they liked best. When they chose, the researchers secretly switched the photos, giving them the photo of the woman they liked least, and asking them to explain why they liked the person in the photo better. Seventy-five percent of the participants happily pointed out the features they liked so much about the face they'd never chosen in the first place. But that's just human beings.
We're leveling up, by showing that humans also rarely really look at the things they buy. The same researchers set up a stall in a store, and asked shoppers to sample tea and jam, and pick which one they liked. Once they'd picked, the choices were switched, and they were given a second taste so they could fill out, on a card, the details that they liked so much about their chosen product. The products were not subtly different. The researchers contrasted flavors like "spicy cinnamon-apple" and "bitter grapefruit," as well as scents like, "mango" and "pernod." Fifty percent of the people did not detect a change. They happily filled out cards that explained why they loved their chosen product so much. (It's worth noting that, while fifty percent of people picking a jam didn't notice a difference, seventy-five percent of people choosing another human being didn't notice the difference. That doesn't say much for humanity. Then again, perhaps more subjects would have noticed a change in their chosen person if the experimenters had said, "This is the one you picked, now put your mouth on them.")
How can you turn this to your advantage? Easy. Give someone a knock-off. Give them a cheap version of what they ask for. Be bold and substitute a present they never even asked for in the first place. Then tell them, straight out, that you were very careful to give them exactly the gift they asked for. You can even embroider the story, telling them you sneaked back into the store and asked the sales person to give you the exact thing they picked out. Tell them it was the last one the store had! Ooooh, they'll be so touched.
It's not technically wrong. As this study shows, at least half of them will be just as happy with the thing they think they chose as they would have been with the thing they actually chose. And if you can give the same amount of happiness without spending as much money or time, then isn't anything else wasteful?