Common fucking sense, for one.
I don't think you understand how this process works...at all.
Actually, you don't understand.
Somebody could order a 5090 from a scalper, damage it, initiate a return claiming the item was damaged during shipping, which leaves the seller with two options:
1. Fight the return, in which case it goes to arbitration with ebay, and ebay will side with the buyer for damaged/INAD (Item Not As Described) cases. They'll forcibly take the funds from the seller and won't even require the buyer to return the 5090.
2. Just do the return, because #1 will happen if they don't.
The seller can then file a police report if they believe mail fraud has occurred, which will result it nothing happening, because the seller can't prove the package wasn't damaged during shipping.
And the best thing about this is, nothing is stopping people from doing it.
If you have a problem with it, then you're probably just a scalper that's scared of getting screwed.