I've worked out how it works, and it's all about the "custom postage"
If you look at the listings, they're all in weird categories like "timber" or "drill presses" or "fire pits".
That's because these categories, where heavy/bulky items are sold, are the only ones that allow "custom postage" instead of integrated Vinted shipping.
So you buy the item, the seller immediately marks it as dispatched manually (which you can do with custom postage) and uploads a fake tracking number/QR code. If you check that code, it may well already claim to have been delivered
There's no integrated tracking because..."custom postage".
Once it's been manually marked as dispatched, a certain amount of time later (usually 21 or 30 days) it gets marked as "delivered" automatically.
The buyer then has just 24 hours to raise an issue. This time of year, that's harder than ever - in 21/30 days loads of people will be on holiday! Not checking their phone, not there to know if it's really been delivered or not.
The scam sellers are relying on people not raising a claim within 48 hours of it being marked delivered.
It's so obvious and I can't believe Vinted aren't doing more to stop it. It's clogging up everyone's feed with scam listings and real sellers' items aren't getting a look in!