Anchoring effect
You see a price and decide in about a second whether it is fair. Fair compared with what? Your brain cannot judge a number on its own, so it grabs the nearest reference point and measures from there, and it will use a number it knows is meaningless if that is the one that arrived first. Whatever a buyer sees first becomes the ruler for everything after it, which is why the dearest item on a menu or a price list is doing work even on the days nobody orders it.
The study
Tversky & Kahneman (1974), Science 185. A wheel rigged to stop on 10 or 65 moved guesses of the share of African nations in the UN from 25% to 45%. doi.org/10.1017/cbo9780511809477.002. Held across 36 samples in Many Labs 1 (Klein et al. 2014, doi.org/10.1027/1864-9335/a000178).
Apple, the $999 that never existed
On 27 January 2010 Steve Jobs stood on stage to launch the iPad and told the room that if you listened to the pundits the price would be $999. By Phill Agnew's telling the number went up on the screen behind him. Jobs let the room sit with it, then announced that the iPad started at $499, and the room applauded. Nobody had ever been asked to pay $999. It existed for a few seconds, as the ruler, so that $499 was measured against it and not against whatever the buyer had in mind before they walked in. Agnew points to it as anchoring done in front of a live audience, with the real price the plan all along.