Several posters on different IBBs and blogs have noted that some BsAs banks will refuse to exchange dollars for pesos if they do not have an account there.

I've personally never had that experience. Of all the different banks I've used, I've found that the Banco de la Nación (at the airport), and BBVA Banco Francés, and Banco Galicia at various BsAs locations give the fastest service.

Note that I always speak Spanish when asking for pesos. I can understand cashiers being unwilling to conduct a transaction if they don't speak English (and why should they ....?).

You will need your passport, and the cashier will often ask where your Argentina immigration stamp is in your passport. And your US notes must be in VERY good condition. No tears or defacement.

John