So far, only one experience buying used from Adorama. I picked up a demo (D) condition 1Dx at a great price, including warranty. It's obvious that someone checked off the list of items that were supposed to ship with the camera and pulled some bits off the shelf to make sure everything was included. It was missing the strap, but I never use the Canon strap anyway so it wasn't a concern. Battery, charger, manuals, eyecup, etc. were all in the original box.
The unit, as received, was flawless visually. Being a demo, it had some clicks on the shutter and a little smearing on the sensor, which took me 5 minutes to clean off (even that wasn't visible in normal images). It was otherwise indistinguishable from new, and for me, a bargain at the price (about half the original list). After about 1000 shots, everything seems to be working well.
Edit: to give credit where it's due, I should add that I talked directly with Manny during the ordering process. I was hoping to buy a new unit but they had just sold the last of their stock; Manny found the demo unit for me and quoted a great price, which I accepted. I don't know that he was responsible for walking my order through to the packing stage, but if he was, even more credit to him.
Oh, and I successfully registered the camera with Canon after receiving it, so there's no question about it being used/returned.