Rubic, that's a great tip!!!

It confirms an impression I had several times when I went forth and back during a day, close to booking a certain flight, leaving booking website X for a while, looking at other sites Y and Z, only to find when coming back to X and doing the same search as before that the price of the flight I nearly booked 2h ago was higher now. Highly frustrating!

I did suspect the higher price was caused by my previous interest on that flight but also always thought 'Maybe others booked that flight in the meantime, so less seats available in that booking class than before, therefore those algorithms increased the price'. Your post not only supports that it might have been myself who the price increase but also offers a simple solution so that it's not necessary to know for sure what the cause is.

Thank you!