All airlines do this all the time.
Set a price alert (using Google Flights, Hopper, Skyscanner, etc) on any route you like and see just how often prices fluctuate.
Here's an example of a KLM route (AMS-TXL; no other airline flies this directly, so while indirect options can be offered, they rarely if ever turn out to be the cheapest) for well into next summer and the fluctuations of the past 2 weeks [I'm waiting for it to sink to €99/€109, as it will eventually]: