It should sound a bit Argentinian. Welcome to Argentina.
I see little old Argentino ladies and men walking up to these guys and doing business with them. I've been in the actual office of one of these places when other Argentine clients come in. US and European women sometimes. Brasilians a lot.
The place you go to do the actual business isn't that much different than the more private "by invitation only" places. Plain, simple, but a bit more in the open. No more dangerous than going to More Money Transfers and walking out with 10,000 pesos, as far as robbery potential. As far as counterfeits, in 6 years, I've never noticed, nor had anyone else notice, a counterfeit that I've gotten from Florida.
The guy on Florida that mumbles "cambio" isn't going to change your money right there. He's just a guy out finding clients since these places don't exactly advertise what they're doing. You ask him the rate, he may ask you how much because the rates differ. Don't tell him how much you have, tell him you want to know how much it takes to get a better price.
If you want to do business, the guy takes you around the corner, still on a street, or into a nearby shop. You're not being taken anywhere strange and suspicious, not up any elevators to an apartment (which is where my private place actually does it). It's usually a little one-room office with a desk, a phone and a couple of chairs and a guy who changes your money.
Not a big deal, really. But to each their own.
Being able to change at a rate well above the official rate has allowed me to cool my heels a little related to thoughts of bugging out because of rising costs, since it means a roughly 30% bump in my real income here.