I recall when the Mac II first came out Northern Telecom bought about 40 of the first ones off the line.
They unpacked the first one set it up and it was DOA. They boxed it up and pulled the CPU out of the second and plugged in the same keyboard, mouse, etc.
Long Story, Short, they sent all 40 back to Apple compaining about QA, etc. When tested they found the problem was one bad keyboard.