2 Years Outdated. Oy...

http://backpack.tf/item/3998548345

Sale 1) Sold for 11 Keys

http://backpack.tf/profiles/76561198025276624/#!/compare/1457938800/1458025200

Sale 2) Sold for 13 Keys

http://backpack.tf/profiles/76561198073592026/#!/compare/1459036800/1459123200 - Buyer's Backpack

Sale 3) Sold for a Steaming Hermes + 4 Gun Mettle Keys

http://backpack.tf/profiles/76561198073592026/#!/compare/1459382400/1459468800

Somewhere between 13 and 16 Keys

Sale 4) Sold + 3 Gun Mettle Keys (3.3) + Spec KS Knife Kit (~2.7) for a Planets Gym Rat (11) + Strange PDA (10) + ~1 Key in Sweets

http://backpack.tf/profiles/76561198137242067/#!/compare/1459728000/1459814400

22 - 6 = 16 Keys

Ruling 11 Keys an Outlier, because there was no trade open for it, and was presumably a quicksell. Let me know if it needs to be included.