I build systems from parts. (I mean, most miners do, right?) Motherboard, RAM, Graphics, Hard Drive, etc. If you can do that, most people who can, know if a system they are building is secure or not.
This is completely false. Building a computer via parts is as easy as adding everything to a cart, purchasing it and snapping/screwing it all together when it arrives.
That is totally irrelevant to if, say, you're aware that newegg shipped your motherboard to the NSA and they had fun with your bios.