Law of supply and demand. Even if the Argentines wanted to get these items by going to a normal ¨authorized¨ retailer today, Apple products have become practically invisible, and not everyone can afford to hop a plane to Miami to get them, this is why there is such a high demand on Mercado Libre for these things and frequent travellers/ex pats who DO travel to the States that could use some extra cash. I dont see anything wrong with it.
I don't consider bringning in 3 Iphones ¨contraband¨ as many executives I know have 2 phones, 1 personal 1 business, and say you were to bring back 1 extra, although I am sure some airport agent might argue otherwise.
I personally have never been checked.