Team Fortress 2
Counter-Strike: Global Offensive
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Sale at 16 keys:
https://backpack.tf/profiles/76561198296101975#!/compare/1507075200/1507161600 - Says traded with 16 keys + 1 Cold Snap Coat, Cold Snap Coat wasn't part of the trade.
Amount of Quickbuyers at 15.2 keys also suggests price increase.
Taking 16 keys.
Finally. Someone with proof.