Many online travel agencies let you book a flight, but they offer only the lowest fare (for ex. Economy Light). On airline websites there often are higher fares (for ex. Economy Basic, Economy Basic Plus, Economy Flex, or even business class ...). Often, buying an higher fare including luggage costs less than the lowest fare (not including luggage) + adding luggage. It is a violation of art. 10 CE 80/2009?
Such law says airlines must offer the same fares on reservation systems where they’re present other than their own website, but it is widely disattended.