I once sent my Spoiler electronics to the mothership for repair, so I know the situation with the US.
The sender has to declare the value of the object (green sticker on the outside of the package, or shipment letter). Dutch customs can charge 25% of the declared value as import duties, and 19% BTW on top of it all, to the recipient. It doesn't matter if it's a second-hand item. And they keep the goods until you pay up. People have said that customs do not check every single item, but a large and heavy box will not escape notice, I think.
Now in my case, if I had declared the package that I sent for repairs to the US, with Dutch customs, then I could avoid taxes on re-importing the same item (or at least be able to re-claim them).
The value quoted by the sender is also the value for insurance - wink wink, nudge nudge ... just be aware that it is a legal offence to quote a price that is too low, exactly because import duties are involved.
Anyway, if you're using regular postal services, insurance never pays out more than 500 euro.
De mazzel!
