People are so dense about this topic.
I've flown in with a return scheduled 6 months later. Occasionally the airline requires a return/onward ticket within a shorter time period. If that happens, I leave the counter, book a flight on Expedia where you have 24 hours to cancel for most flights(indicated when you select a flight), and return to the counter and proceed. After I'm through there and at the gate, I cancel the Expedia flight. No costs, no problem. And if immigration asks, you now have the canceled Expedia ticket to show.
I do show up to the airport an hour earlier to allow enough time to do this if necessary.