How come I regularly see third-party OTAs offer the same itineraries cheaper than the airline then?
Sometimes there's a mystery fee added just before payment, but not nearly always – and I've flown such itineraries once or twice myself (if the difference was significant and I was absolutely certain I wouldn't need any change or extra service).
I was under the impression that these effectively share part of their agent fee with the traveler as a form of kickback (to appear as the cheapest option in search, which in the end might end up a win-win for both).