Why do flight search engines give inconsistent results?

Question

I've been shopping around for flights, and I've noticed that a few flight search engines such as Skyscanner and, in particular, ITA give inconsistent results.

I don't know if this applies to all flights, but in the instance of my trip, ITA shows cheaper results if I choose "plus/minus 1 day" option instead of searching for those three days independently, all else the same. In another leg of my trip, the opposite happened. I was able to find cheaper flights by searching "on this day only" option, and when I chose "plus/minus 2 days" or "plus/minus 1 day", the cheapest options from the "on this day only" option did not show. Why is this and what is causing it? It's making me wonder if I'm actually getting the best possible deal.

I have had similar experiences with Skyscanner, where the price will actually fluctuate a little within a matter of a few hours.

Answer 1

ITA has a 60-second time limit on its searches, so if any of its sources takes longer than this to return a result, those results are not included in the end-result. If that happens, and you do the same search again, even immediately, you can get drastically different results if one of the previously-slow sources responds faster.

Undoubtedly every aggregate search engine has a time limit, although exactly what the time limit is, and how its implemented, is likely to vary drastically.

But this is likely a major cause of an appearance of fluctuating prices.

Answer 2

Anecdotally, I've heard that some search engines detect your first search (with cookies or whatever) and give you a very low price and then when you come back to book, the tickets at that price are sold out and they charge you their profit margin more.

They claim it's false, but the sites certainly seem to behave that way at times.