Originally Posted by number_6
Airlines go after chronic offenders -- people who have dozens or even hundreds of round-trip flights and always throw away the return coupon, for example. ...
The Brazilian government does this systematically, at least for all students and staff of Brazilian universities who will be staying abroad more than three months. They actually issue two round-trip tickets, one with the correct departure date and the other with the correct return date. This has been doing this for at least 10-15 years.