I understand you get a better exchange rate in the blackmarket "dollar blue". But how does it work and how do you ensure your personal safety?
The way it works, well, it's pretty easy. Since we can't buy dollars in the official markets due to restricting laws, there's a blackmarket when the exchange rate it's obviusly higher. Usually there's people near the exchange banks or "arbolitos". I do not know a lot about Buenos Aires because I don't live there, but the Florida street it's pretty famous for having a lot of arbolitos and being easy for foreigners to spot them. If you know basic spanish, this web page might help you with the current exchange rate in the blackmarket.
The place to get the best rate is Florida St, but there are so many people their to change with it is hard to know who to trust. The way I found best was to find someone who has had a good experience changing money with one of the shops there and get them to take you to the same place. There will be people at your hostel or hotel who will have changed money at places that they can tell you about. It is worth doing some research on spotting fake Peso notes because it is a common problem, and don't change all of you USD at one time. Checking the Dolar Blue website to know what the rate should be is always smart before going out to change, and knowing that you have some negotiating power.
In reading up on changing money before going to BA I got kind of nervous because a lot of people make it out to be quite difficult and sketchy, but I found that it was pretty easy, and since so many people are doing it there is usually a friendly person at a hostel of language school to take you to a place they have recently changed money. Instead of being nerve racking I actually enjoyed the process.
Another thing to note about BA is their is a common scam with taxi drivers where they take your notes, quickly switch them with fake ones and then refuse to accept them. Since fake notes are so common this is a good way for taxi drivers to pawn them off on tourists. Make sure when you are taking a taxi that when you pay you never let the bill out of your sight, or make a note of the serial number before you hand a 100 peso note to a driver.
In Argentina usually is sure to get exchange in any place, be sure to go to a physical location, not the "arbolitos" (people in the street offering change) they pay less.
If you want to feel safe, go somewhere where there is movement of people.
Try talking to the hotel manager to advise you or people who are in your same situation.