Real estate agencies used to charge one mont's rent as their fee in low to mid-range neighborhoods and up to 2 month's in high rent districts. But now 2 months has become the norm. Do I think it's right? Not really but in New York City, my home town, if you rent they charge you 15% of the 1st years rent, plus 2 months security and many new buildings require a guarantor if you are in your job for less than 2 years or under 30 years old. Real estate agents make 90% of their income from commissions so they try and max out every transaction.
Also if you don't have a guarantor here in Buenos Aires, you are going to pay A LOT more than the norm, and you have to understand, if they rent to you, and have no recourse if you damage, steal, don´t pay, they are going to charge you more for that risk - it's due to many bad tenants and horrible stories of taking months and lots of money to evict someone who doesn't pay the rent.
It happened to me a few years ago, I had a rental property, rented it to a "friend" he paid me the 1st month's rent and then stopped speaking to me. It cost me $7,000 pesos in lawyer's fees to get him out and he did $10,000 pesos worth of damage to the place - in the 6 months that he was there. Not to mention the loss of income (I had to sign an agreement NOT to sue him for the unpaid rent, in order for him to leave), and the emotional anguish of having to deal with a justice system that sort of laughs in your face when you try to do somebody a favor. So I´m sorry to hear all the money being charged but I would NEVER rent again to someone without a guarantía, 2 months upfront and the real estate agent makes up their mind what to charge in commission - I don't really have a say in that.
Read the "Ley de Alquileres
http://infoleg.mecon.gov.ar/infolegInternet/anexos/25000-29999/27287/norma.htm Ley 23.091" and you'll see just how in favor of the tenant things are here.
I am totally neutral on this issue but having dealt with being a landlord here, I understand why there is SO much distrust.
Good luck!