I ship Internationally.
My only advice is that by law you *should* mark 'merchandise' on your custom's forms. Checking the 'gift' box is not only breaking the law, but is dishonest. A gift is like sending a sweater to your Mother. They bought it from you, it doesn't matter if they are giving it to someone else, it is not a gift.
I researched this one on the government sites and discussed it with our Post Master years ago.
Thus, I would also suggest making sure in your listing terms that this point is mentioned so that it is not a big surprise for the buyer.
That is my only word of wisdom.
