Nikad's advice is great. When the buyers pay by Mercad Pago they can either use a credit card (and the payment will be shown immediately) or in cash at Rapi Pago or Pago Facil (among others). Buyers have several business days to complete the payment by Rapi pago and Pago facil . Be sure the funds have been credited to your Mercado Pago account (even thought they are not yet available for you to use or withdraw) before you send the package.
With Mercado Envios the buyer will have paid the shipping cost in advance and all you will have to do is print the shipping label (aka coupon) and take it to the sucursal of OCA or Correo Argentino to send it. If you are sending the items in used boxes by Correo Argentino you have to wrap the package in plastic or paper to cover any printing on the box. OCA does not require this.
Be sure the payment is credited to your mercadopago account before you send the package. It will appear as no disponible (not available) until the buyer receives the item and makes a positive rating for you. Buyers have 20 days after the purchase to make the rating or initiate a claim (aka reclamo) if they are not happy with the purchase.
The funds will become available as soon as they make a positive rating. You then have the option to use the funds for purchases on Mercado Libre or to transfer them to any bank account in Argentina. It does not have to be an account in your name.
Mercado libre has a commission free category. Your items will get less exposure, but if there are buyers searching for the camera lenses of the same brand you are offering for sale they should find them easily.
It is more difficult to sell items like camera lenses (especially expensive ones) if they buyer cannot see them in person before making the purchase. The fact that you have no reputation as a seller and will be new to Mercado Libre will also be a hindrance.
I suggest you search ML to see if there are any listings for the same model and "size" of the lenses you have for sale., keeping in mind that high asking prices provide little useful information. Unfortunately, Mercado Libre does not have a feature which displays the actual prices of previously completed sales (like eBay has).
You can add any publications that feature lenses similar to the ones you have to a "favorites" list by clicking on the heart and then check s often as you wish to see if they have been sold (finalized). Even if the publication is finalized that doesn't mean the item was sold. You'll have to view the original publication to see if there was a sale.
One way to overcome your lack of a reputation as a seller and the problem of distance would be to offer the buyer a guarantee they they will be 100% satisfied or may return the item(s) for a 100% refund.
You would have to agree to pay the return shipping costs but they could be much higher than it cost to send the items by mercado envios and the insurance would be extra (I think 2% of declared value) .
I think most buyers on Mercado Libre are "bottom feeders" looking for the best buys they can find.
I know this because I am one of them.