I agree with Gaucho's good advice. While it's feasible it will be quite time consuming and requires a local connection because, even if at the end you settle in cash, Mercado Libre forces you to offer the Mercado Pago option, their own version of Pay Pal, which must be linked with an Argentine bank account.

Also ML is very popular with people in the provinces, which means you should offer some sort of shipment to your client's address, either Correo Argentino, OCA or Andreani, all of which you should settle on your own.