This is the general mantra of Bunnie Huang's book The Hardware Hacker. He goes into lots of detail on why you need to be on-site, all the things you can expect

This is the general mantra of Bunnie Huang's book The Hardware Hacker. He goes into lots of detail on why you need to be on-site, all the things you can expect to go wrong/get misinterpreted, and red flags when shopping factories. It's a really captivating read if you're interested in the minutiae of hardware manufacturing.