"[...] MercadoPago will surely turn people to cash payments, as not everyone can afford to wait a whole week for the payment to be credited to the seller, which is often only across town in the same city. µ "

You're completely right. Most Internet buyers out there, want their products shipped in the same day. Or else, they can change their minds or even get out of their houses, take a bus and buy the product in a well known shop.

This reminds me, about the Paypal + Visa problem in Argentina a few months ago. What the h*ll was that? 

Argentina fails in this approaches because it will never recognize that it has some 50 years in delay...