It seems to be standard that they do so to check that VAT is actually paid. When they then (probably, unfortunately according to their own experience) cannot see that VAT is paid, you are prompted, to avoid the package being returned, to pay VAT again for the same purchase! You are then allowed to contact the person you purchased the item from and ask them to pay back the VAT you paid in the first round. You must then send a copy of the receipt for your second VAT payment and proof of receipt of the package. (example applies in case of ebay)
If someone is aware that the process is actually working properly, it would be great if this could be shared in the thread. Two packages have been passed right through for me, but that was because the shipments had (incorrectly) been declared as poisons. I have paid VAT and therefore have a clear conscience. However, the system does NOT work! U fnRight here, I don't know. But the process is basically the same as when returning outside the EU. If you have to fill in a pious one and be able to show that you have received/sent in return the watch, the pluring is paid back. However, not the 75 KR they took in admin. Duck