Clearing your cookies will not make the flight cheaper

You open a private window, clear your cookies and check the same flight one more time before buying. If that sounds familiar, what follows is a review of the product you are using.

WHAT IT PROMISES If the search engine does not know you have already looked, it cannot punish you. The extended version includes wiping your history, switching browsers and, in the more devoted forums, searching from somebody else's phone.

WHAT IT DOES Nothing measurable, and it is worth saying where that "nothing" comes from. In 2014 four researchers from the University of Leuven and the French institute Inria presented, at a privacy workshop, a paper with an honest title, "Crying Wolf?": they watched the fares of 25 airlines from different profiles for three weeks and found no systematic price discrimination based on the user's history. Two years later, in 2016, the American magazine Consumer Reports tested it the blunt way: 372 searches across nine sites, a clean browser against one loaded with history. Forty-two pairs of prices came out different, and here is the detail that finishes off the myth: 25 of those differences were more expensive on the CLEAN browser, by up to 121 dollars, and only 17 cheaper. Consumer Reports said it could not attribute either result to browsing history.

Where they do watch you is hotels. The reference study on price personalisation, the one a Northeastern University team in Boston presented in 2014 after shopping on sixteen sites at once, did find different treatment for hotels and car rental: Cheaptickets and Orbitz showed logged-in users cheaper hotel prices, while Expedia and Hotels.com steered a slice of their visitors towards the expensive hotels through an A/B test. And it left airline tickets out of the sample on purpose, with an explanation that is half this article: the price of a flight is not set by the website you are looking at.

WHAT DOES WORK (AND WHY IT LOOKS LIKE THE OTHER THING) The price of a plane ticket is not set by a person watching you: it is set by inventory. Every flight is sold in fare buckets, groups of seats at the same price with a fixed number of places. When the cheap bucket runs out, the system opens the next one and the fare jumps, all at once, for everyone arriving afterwards: for you, for the person who has never searched, and for the person searching from Tokyo. Since that jump tends to catch you on your second visit, you read it as a personal reprisal.

On top of that there is a silly effect: the search engine sometimes shows you a price that has already been sold, cached from an earlier query, and the real one appears when you reload. That is not surveillance, that is cache.

One honest caveat, because it is real: the country you buy from and the currency you pay in do sometimes change the amount, because taxes and fees differ by point of sale. That is not cookies, and clearing them does not touch it.

VERDICT As a money-saving tool, zero. As a ritual that makes you feel you did something before spending 180 euros, it works perfectly.

Next time, swap the ritual for the calendar: in the search engine, open the whole-month view instead of the single-day one. That shows you which dates still have a cheap bucket left.