Upload & Sell: Off
Amazingly, the same thing recently happened to me. I shipped my 5D3 to Canon to check the AF system. They received it and confirmed the problem, and I expected to get it back a couple of days later (as is usually the case). However, after a week I began to get suspicious. I called the help line, and the reps I spoke with in Virginia just kept saying "the Irvine service center is very busy; give it a few more days." After more than ten business days I knew something was wrong, so I asked to speak with a supervisor. This started another several days of back and forth until it was revealed that they couldn't find my camera. So, they replaced it with a brand new 5D3 and I have a 1-year warranty. Better yet, my camera now focuses properly!
All's well that ends well. It's a shame they lost it, but they handled it well once that became apparent.