Gotta build it.

Sale 1: Sold with Strange Specialized Killstreak Australium Force-A-Nature[14 keys via mini] for Circling Peace Sign Sergeant's Drill Hat[30.5 keys]

http://www.tf2outpost.com/trade/27918805 b/o was 15 keys

http://backpack.tf/profiles/76561198254377432#!/compare/1457683200/1457769600

30.5-14=16.5 rounding to 17 keys

b/o was 15, capping it there.

Sale 2: Sold for 11 keys+sweets around 0.5 keys

http://backpack.tf/profiles/76561198046838964#!/compare/1456992000/1457078400

11+0.5=11.5 rounding to 12 keys

Sale 3: Sold for 12 keys

http://backpack.tf/profiles/76561198043979442#!/compare/1458111600/1458457200

Sale 4: Sold for 12 keys

http://backpack.tf/profiles/76561198127530992#!/compare/1459209600/1459468800

Mini on Force a Nature:

Sellers at 14 keys https://gyazo.com/dfdd992185f7633e55774fa3633df68b.png

Seller

http://www.tf2outpost.com/trade/27919939 14 keys for 1 month

I have sales at 12, 12, 12, and 15. I also have a seller at 14, due to the seller, I'm going to call 15 the outlier here. Making this 12 keys flat.