Many Argentines are like that. I know someone who just got SERIOUSLY cheated - lost all his savings due to corruption. Not his fault at all. There are good people but most don't seem to have consciences and have no interest it how cheating affects other people. I don't think it is worth taking this to tax authorities, etc. You aren't going to change a culture. I would tell the owner that I'll pay the official rate to BUY dollars at the time of payment. That's all. Then if the owner is not happy, leave. Ask for your money back. If you don't get it then tell her you are going to the Secretary of Consumer Defense and the tax people. She'll give the money back. Do you really want to rent from this creep? If she is like this now she is going to find other ways to cheat you - maybe won't return security etc. I'd find another place.