Earlier quoted context omitted.
But how do I trust the independent parties?
The same way you trust anybody? If you're so paranoid that you believe literally everyone is out to get you, then you're not going to be able to function in any society, let alone one as interconnected and interdependent as our own.
You can hash the source code and verify that what you have is the same that the developer shipped.
There is no hash function for hardware.