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Maybe this is part of the clue

"AC Adapter and Wall Adapter as picture (no manual and not in original retail packing..(USB-C Charge Cable is not included)"

So where did they come from ?
 
Personally, I wouldn't. You've spent a lot of money on a Mac, I'd go for a genuine Apple 29w charger. The USB cable however, I would look for cheaper alternatives, but from well known brands such as from Belkin and Anker.
 
I checked a recent ebay purchase of Apple's latest wireless keyboard as I got it for $60 instead of $100. Turns out it was sold by a charity. Item works flawlessly and was new in box with packaging.
 
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