Your post isn't hugely clear, tbh. There seem to be a few issues at play.

You do not have anything in the description to say that buyers should contact you for a postage quote before purchasing. If you're expecting people to wait for an invoice with postage added on, without them knowing upfront what the costs are going to be, then you're going to have continual problems. It is very easy to work out the international postage for most destinations and then apply it in your postage policy. That way there are not hidden costs for the buyer.

In fact, it would be entirely reasonable for a buyer to assume there are no additional costs/postage costs associated as nothing comes up when they choose their destination country. For example, clicking on the USA drop down in the postage calculator just says that you will post within 2 days of payment. 

There are a number of other problems with your listings. In the one I looked at, you say no postage to Italy, Germany etc, but they are actually still part of your postage locations and have not been excluded.