[t0mas88]

In the Netherlands buying stolen goods is a crime. If you knew or could reasonably have known it was stolen (e.g. a bike with a broken lock, no keys and a low price) you risk a serious fine. If you didn't know it was stolen you just loose the goods. Technically you then have a claim on the seller, but of course you're not going to get anything.

So stealing your own thing back without the police involved may technically be illegal, but practically if the airtag tells you where your stolen bike is and you have the keys, skip the police and take it. Nothing will happen. The thief or their client is not going to call the police since that gets them arrested or fined.

Of course you can't go into the thief's house to retrieve your things. Then you do need to call the police first. But the one case I know about someone doing that for a stolen iPhone based on Find My app location, the police showed up quickly and arrested the thief + found lots of other stolen things in their possession.