Just got back from a week in BA. Our first hotel, in Palermo, directed us to a storefront a few blocks away that gave us the blue rate and crisp new bills.
A few days later, our hotel in San Telmo would not make any suggestions. We went down to Florida Street and found the many people calling out "cambio, cambio". We stood and watched for a while and saw multiple people exchange money on the street. At one point, a federal police officer went up to talk to the people doing the exchanging, then walked away. We did a small exchange at a good rate (better than the storefront) with no problems.
I certainly had mixed feelings about the whole thing.