score:5
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.
Upvote: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.