It is unfortunate that they left you a 4 star for reasons not of your own. However, their comment is left in Spanish, so a large number of people cannot read it. From what I can tell, ( thank you Google Translator) it basically says:
"Good workmanship and design, maybe some delay on shipping, but for reasons of Italy's post. It was a good choice choosing this store."
Not a bad review overall, but most won't know that.
Once you get a few more sales, the number will go to 5 stars as the 4 won't lower your overall average. You could always contact the buyer and explain how thrilled you are they liked the item, and being that you are a new shop owner, you would like him to have a 5 STAR EXPERIENCE!
You have the option of responding to the review also, and I would do so in English as well. Saying nice things about the buyer and your disappointment in the shipping time would be the way to go
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http://www.etsy.com/help/article/4587?ref=help_search_result