Of course things you owned, left the country and are returning with are exempt.

Import Duties apply to items purchased while outside the country and that you are returning with.

If you were away long enough to establish residency, there are usually exemptions to items of personal property you are bring back with you.

The duty-free allowance is different for every country, but in Germany for example it is around 450€ per person (the exact number escapes me). Any goods you return with in excess of that amount is subject to duty.. Some items you return with are always subject to duties.

In Germany for example, they very much will check for this and enforce it.