Agents and consolidators can have privately negotiated fares that are not available on the airline’s own website. They can add their margin and still sell the ticket cheaper than the airline’s published fare. They also make money from additional products , insurance, luggage, seat selection, meals and other extras. Prices also depend on the season, route, availability and when you book. I have found cheaper one way tickets when I do not have a fixed plan, but for direct flights, a round trip booked in reasonable time is usually cheaper, especially if you are looking for flexible tickets or higher fare classes rather than just basic economy.