A tech expert has warned prospective holidaymakers to be weary of 'dark patterns' when booking flights.
Harry Brignull, a internet and technology expert, has described how some airlines use tricky techniques to encourage passengers to pay more for flights.
'Dark patterns' refer to the way booking websites are designed, to use nudges and notifications, to encourage customers to make a certain choice.
They are not the same as the dynamic pricing model which many airlines use to determine how much a plane ticket costs, based on the demand for the flight.
It has widely been suspected that these prices rise and fall depending on whether you've visited the site before, although this has never been conclusively proved.
Rather, dark patterns are little psychological tricks that don't actually impact the price of a ticket, but can encourage customers to buy.
Mr Brignull said that the tricks can be subtle and are sometimes "intended to gaslight the customer", BBC Worklife reported.
A classic example is when you're looking on a booking website - whether that be for plane, theatre or coach tickets - and a ticker implies there's a great deal of demand for the one you're looking at.
The number is designed to make users feel as if there's a degree of urgency when it comes to them booking.
For example, when you book a flight you may see a notification or pop-up informing you that 20 others are looking at the same one. That number is highly unlikely, and may be due to a 'dark pattern'.
You may be fully aware that this number is unlikely, but it's difficult to resist the psychological trick.
Mr Brignull urged people to be aware of the tricks, as knowing what booking websites are trying to do to you is the only way of resisting, as well as calling out companies for using the practice.
"If you know what cognitive biases are and the kind of tricks that can be used to change your mind to persuade you to do things, then you're less likely to have them trick you," he told Wired.
"Complaining quite vocally is a very good thing. So don't complain by email when no one can see it, instead complain in public, then you're more likely to get a faster and more efficient response."
Rory Boland, Which? travel editor, has called out the practice: "Despite work by the Competition and Markets Authority [CMA] to clean up the industry, we know that not all hotel booking sites are following the rules.
"Until the whole industry complies with the rules the CMA has introduced and makes the necessary changes, UK holidaymakers are still at risk of being misled by unscrupulous practices."