Round trip required?

The immigration of a country might have requirements for ongoing travel, but not an airline.

Really, is an airline in a position to deny boarding to a person who says, “I’m flying to Mexico and driving back with a friend.”?

And if an airline were to try to impose such a requirement, the time to advise the passenger woukd be at the time of selling the ticket. “I’m sorry, but we cannot sell you a one-way ticket.”

Now, who are you going to believe? A friend, or some anonymous stranger on the internet?