Searching for the same flight twice and seeing a higher price is a common experience, and it is generally blamed on tracking. The likelier explanation lies in how airline inventory is priced and how search results are stored.
Seats are sold in buckets, not at one price
An aircraft cabin is divided into fare classes, each holding a limited number of seats at a set price, with cheaper classes filled first.
When the seats in a class are gone, the next quote comes from the class above it, which is a step up rather than a gradual increase.
A fare that jumps between searches has usually crossed one of those boundaries, either because someone bought a seat or because the airline adjusted the allocation.
Allocations move continuously
Revenue management systems reassign seats between classes throughout the selling period, responding to bookings, competitor pricing and how the flight is filling against forecast.
A flight ahead of forecast has cheap classes closed, while one behind may see them reopened, which is why fares fall as well as rise.
These adjustments run automatically and frequently, so two searches minutes apart can genuinely return different availability.
Cached results explain some of the difference
Search sites do not query every airline in real time for every result, because the queries are expensive and slow.
Many results come from stored data refreshed periodically, so an attractive fare shown in a list may already be gone when the booking is attempted.
The price appearing to rise at the point of booking is often the moment the site checked the live system for the first time.
The tracking explanation is weaker than it sounds
Airline pricing is driven by seat inventory that applies to all buyers rather than by individual browsing history, and fare classes are published to the systems that distribute them.
Currency, point of sale and membership status do produce different quotes, and those differences are visible and rule-based rather than personal.
Clearing cookies changes little, because the fare came from an inventory system that was never looking at the browser.
What actually moves the price
Departure timing matters most, with fares generally climbing as the date approaches and the cheap classes are consumed.
Day of week, routing, connection choices and the airport used change the answer more than the moment of searching does.
Watching a route over a period gives a sense of its normal range, and that range is a better guide to whether a fare is good than any single comparison.