Almost all countries levy custom duties (with an allowance) on imported goods by passengers, such as electronics, clothes, etc., that have been bought from outside that country and are intended to stay there.
I am an EU citizen (Germany), and once when flying in from a non-EU country I was stopped by a customs officer who thoroughly checked my bag. I had a few new shirts and shoes (with removed labels), and they didn't ask anything, even though the apparel was obviously never worn. The value was around the tax-free €430 allowance, or it was even exceeded.
However, another time I was in an opposite situation when I was not bringing anything new. I had a hard time explaining that my camera and clothes are not so new, and have been bought in Germany/EU, and not during my trip outside the EU.
Can someone explain how does this work? How do custom officers determine if the imported goods of a passenger are old or newly bought? How do passengers prove that they did not buy the goods during the trip? Since people do not carry receipts of all the things they have with them, I don't see how it would be possible to prove that something fairly new was not bought during the trip.
It is not unknown that many people tend to remove the packaging and/or tags of new goods to conceal that the goods are being imported, but there are also people who travel with new goods which have been bought shortly before the trip. How do customs officers distinguish the two?