> As soon as your shipping value exceeds a treshold (IIRC about 1000€), you have to electronically declare the customs.

The threshold is zero in my experience. I volunteer with a small non-profit publisher, and last year we shipped a few hundred magazines to Europe but with the wrong customs labels. These are black-and-white technical journals shipped in clear plastic, so even with missing labels, they very obviously have almost zero value.

But because we had the wrong customs labels, about half of them were held at the border and our members had to pay the duties themselves, since it was too late for us to pay them. I think that one member had to pay almost 20€: 0.20€ in VAT, plus 19€ in "fees". We sell the issues for $4.50 each (plus shipping), so it was quite a surprise when we started hearing about how high the fees were.

This isn't due to inexperience either, since we've shipped ~1k copies to Europe every year for over 40 years. But we had just switched shipping providers, and our new provider had just written "magazine" as the label without any further details. For the next shipment, we added a proper customs code and prepaid the duties where possible, and that seems to have solved the problem.