Here's the master thread on this subject:

http://www.flyertalk.com/forum/argen...a-flights.html

A condition of the cheaper resident fares is that you are an Argentine resident and you may be asked to prove this when checking in. If you can't, you forfeit the ticket and will not be able to fly unless you buy a walk-up fare. Some non-resident FTers have reported using these fares without problems but if you go down this route, you need to be aware of the risks.