Booking directly through the airline usually allows for some sort of seat discrimination. But as most flights are booked through various aggregators, the strategy that seems to work is to offer a dirt-cheap basic ticket, and then hope to upsell the customer on premium seating at check-in time.

Only recently have aggregators started disclosing bag charges, which could be significant, especially with low-cost airlines (WOW, Norwegian, AirBerlin) outcompeting everyone else on basic ticket fare and appearing high in the results.