Bests & Worsts Reviews from Amazon

I purchased this unit for my son's birthday. I bought it new for full price. A used unit arrived. In addition when we opened one of the boxes for the parts there was a note inside from the previous owner. See the photo. I have been a monoprice client for several year, long before they started selling on Amazon. I have lost all confidence in them. I guess they should stick to wires. This is plain lazy, shoddy work. On further inspection it appears AMAZON IS THE GUILTY PARTY. I FOUND ANOTHER CUSTOMER's RETURN LABEL IN THE BOX.