This is excellent advice which I also follow. When I get large denomination bills from an ATM, I only break them at a large supermarket (where the cashiers will carefully scrutinize them). I've only ever wound up with a few fake coins.

It's known that the professional forgers are concentrating on 50 and 100 peso notes, and for a foreigner they will be difficult to spot. There are also forgeries of US$100 bills. Interestingly the US Treasury estimates that there was US$50 billion in (US) currency in circulation in Argentina in 2006.

Taxi cabs, at least in BsAs seem to have a bad reputation for passing fake currency, not just to tourists (from anywhere outside Argentina), but also to locals. I've had several Porteno friends end up with fakes when it's been late at night and difficult to evaluate the currency.

John