Even compiling from source, one also has to trust the compiler...
(see, e.g. the classic http://cm.bell-labs.com/who/ken/trust.html, pdf version at https://www.ece.cmu.edu/~ganger/712.fall02/papers/p761-thomp...)
And the chip design, and the fab control software, and the tools that make the tools that make the tools. And descrete components won't help you because transistors are large enough to conceal a mircocontroler emulating a transistor and listening for high-frequency handshake signals.
Relays are probably safe since you can make those yourself out of iron and copper (rods, springs and wire), and conveniently those are the same things you need to build motors!
You're still probably screwed though.