The running joke is a joke indeed, we have accountability and traceability in our marvelous high-tax socialist haven, if you pay someone a significant amount it's VAT has to be tracked, parts can't just magically appear out of thin air, well maybe every now and then, but not systematically.
Edit: Especially airbags, they require special certifications to be installed and managed in Sweden, second hand airbags is NOT a thing here. Though other parts very well might be.
In my country, if your car is missing (say) a wingmirror, you can go to a 'scrap dealer' who has a yard full of written off cars, and they'll sell you a wingmirror taken off a scrapped car.
There isn't any greater authority, keeping track of every car part or ensuring the number of wingmirrors leaving stock matches the number legitimately entering stock.
We're not talking wingmirrors, we're talking interior. And it's different for cheap stuff one could pay cash, but cars are registered when they come in to the junkyard and parts sold are declared.
I'm not saying it can't happen every now and then, but it wouldn't work systematically.
Edit: Especially airbags, they require special certifications to be installed and managed in Sweden, second hand airbags is NOT a thing here. Though other parts very well might be.