mizzmarr, you're right. You need to show your DNI and:
When boarding, the passenger will be asked to provide documentation confirming his or her residency. A passenger with a ticket for this class will not be boarded if her or she fails to provide said documentation.
In
http://www.transporte.gov.ar/aero/usuarios/tarifas.html there is a chapter TARIFAS PARA RESIDENTES.
In short: There goverment fixes for each route a min and max fare/tariff (related with the bus costs). These fares are relatevely low, and the companies receives compensations.
There explains than the min fares are not always profitable and the companies muest offer the 20% off the seat at the MINIMUM fare, only for nationales. So foriners pays the full price.
But just one remark: this is not only same ticket with different price, there are differenets fares:
Examples:
Changes before departure:
Locals: (Tarifa BASE) $100ars fee
Flexible: Allowed (free)
Changes after departure_
Locales: Not allowed
Flexible: $100
Refunds:
Local: $150 fee
Flexible: $100 fee
Milleage programs:
Locals 25%
Flexible 125%
I hope to be usefull for you