Savannah here from the Shopify Guru Team. :)
The available payment gateways list applies to your country and currency, but not to the country of your customer. You should be able to sell and ship to customers internationally, regardless of which payment gateway you've integrated with your shop.
Have a great day!
Savannah | Shopify Guru
So, If a customer from USA come into my webstore, add a product to the cart, then go to the checkout and pick the credit card gateway that i added (for instance MercadoPago, that is not in the USA gateways list), could he make the purchase normally?
Thank you very much for your response.
Great to hear you are trying to sell like a PRO.
Go to usabox.com, sign up and create your own P.O. Box, that will give you an USA address, it's free to have it.
The only time you'll have to pay is when you have a return, for the days you hold the product inside the box. And if you have to ship it.
But for having the address, is completely free!
And then you can add that address to your store pages, email footers, and wherever you want, except for the general settings in your shopify dashboard, where you need to place your real address.
Hope it helps! Otherwise, let me know.