In Europe, Vueling (a ULCC) is masterful at the upsell. If you choose the cheapest, ie Basic, fare, you’ll be offered seat selection at a price, earlier boarding at a price, lounge access at a price, prepay your luggage fee at a better price. Not only does that all help them capture ancillary revenue, but the explicit upsell also makes it really, really clear of all the things with a $ value that you’re not getting in the fare that you paid.