At the very least, it should be illegal to use the misleading tactics they use for things like seats. Not sure if airlines in the EU differ (I'm Canadian), but seemingly every airline here tries to make the seat selection seem like it's mandatory. While I've never fallen for that, I wonder how many people pay for their seats simply because they didn't realize it's possible not to?

And Flair here in Canada is the budget airline whose whole thing is that they advertise prices that don't include a carry-on (which is standard with every other airline in Canada). But if you want a carry-on, they'll charge so much that their flights are often roughly the same price as the competition (and they push bundling carry-on + checked bag so that people will pay more than they need). Flair is great if you know what you're doing, since a backpack fits the "personal item" size limit and is all I need for short trips, but many people don't realize how it works and think they have to pay for the carry-on, plus Flair gets their listings to show up higher in search results because they will list the base price. Google Flights makes it clear that there's no carry-on, but it still shows those flights first and someone without familiarity with Flair won't expect carry-ons to cost as much as they do.