How to get the cheapest air fares
Before you start looking for the cheapest flights online, make sure you set your Internet browser to private browsing or Incognito mode. You can usually do this in the Settings area. This is the best way to get cheap deals.
Source: History A2Z
This is because your browser can track your internet usage patterns through website cookies. These cookies let companies know what you are looking for which makes them mark up the price when you check again.