How to really compare flight prices

The total cost, not the base price

Before comparing two fares, add to the base price the cost of checked baggage, seat selection, and any extras: a seemingly lower fare can become the most expensive once these elements are added.

Price history: Google Flights graph

Tools like Google Flights display a graph that places the current price on a scale between "low", "average", and "high" compared to the historical performance of the route, and allow you to activate an email alert when the fare drops significantly: a more reliable indicator than the simple feeling that the price is "good".

Times and layovers weigh as much as the fare

A lower fare with an inconvenient layover or nighttime departure can turn out to be less advantageous, once you account for lost time or a possible overnight stay, than a slightly higher but direct flight.

Change and refund conditions

Two tickets at the same price can have very different conditions in case of modification or cancellation: it's worth reading them before purchasing, especially if your travel date is not yet certain. When you really deserve a flight ticket refund depends on precise rules, different from the commercial policy of the individual fare.

Before booking, open the historical price chart of the route on Google Flights: if the current price shows as "low" compared to the average, it's a more reliable signal than simply comparing two numbers.