Hijacked account -> Hijacker -> Overslop -> Tradee
Hijacked account gets all items back
Hijacker (First person who receives the items off hijacked account) banned
Overslop refunds money to tradee
Tradee doesn't lose out on anything
This makes more sense, Overslop will lose out, yes, but at least he wouldn't be banned, and the person who actually hijacked the account would be the only one made to suffer.
You're making a pretty huge, and probably flawed, assumption there. I would assume that the hijacked account would have traded directly to Overslop to avoid this issue in the first place. Or if not the items would have been traded to an empty account made purely to act as a mule, so banning it wouldn't do anything.