When I was in Argentina a few years ago there were money changers peddling dollars on every corner in downtown Buenos Aires, at a time this was illegal (Cristina was president).
If I remember correctly, it was referred to as the "black rate". If you paid a vendor in USD directly, you got the "blue rate". Both of which were much better rates than the ATM.
Instead people who need to exchange regularly go to "cuevas" (caves) which are just hidden and illegal currency exchanges that have much more volume.