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Optimal as you mention is a country specific domain, each hosted on a server in that country and you go into Google Webmaster tools and designating the country for that site. Take a look at what Google states http://support.google.com/webmasters/bin/answer.py?hl=en&answer=182192 Even though you could setup one site and then setup the different country sections under different subdomains etc, it seems like they are suggesting having domain specific sites is the best option. I think if you show them that "This is what Google suggests", that should bear some weight. All that aside, the strongest argument comes from the user side of things.  If I am an american, will I go to a site from Spain to find what I need.  Probably not.  Unless they have customers who expect to visit a site in Spain to get a product, the separate TLD would make sense.