After receiving complaints, Google changes its trade-in kit so incoming handsets are more protected
Considering that the terms of the trade-in deal say "refund is based on phone received matching the description provided at time of estimate," damage to the trade during shipping could have resulted in the whole deal blowing up in a purchaser's face.
Google has remedied the situation by sending a new trade-in kit that features a cardboard box that while thin, comes with thick foam padding inside. The new box was greeted warmly by some posters on Reddit, and it should allow for the safe arrival to Google of a handset being traded in for a Pixel 2 or Pixel 2 XL.
source: Reddit via AndroidCentral