No, they auction off returns in mixed boxes. Here's a video of someone who bought one: https://www.youtube.com/watch?v=kTaYet07Ioo

No, as I understand it they sell job lots of returns on a pallet or whatever, by weight or volume I'm not sure. More valuable/branded stuff is sold for what it is though, and direct to consumer, in the 'Amazon Warehouse' section - at least, iirc it advertises itself as products returned or damaged in the warehouse.

I've received duplicate items some times, like when I report something not received and they send me a replacement that arrives the same time as the original missing item.

I've offered to pay for stuff since it saves me the bother of buying it again some time in the future and the reps will go out of their way to make sure I can't do that. Even to the extent of saying they've charged my card when they actually haven't.