Sale #1:

http://www.tf2outpost.com/trade/25728101

Sold for 18 keys

http://backpack.tf/profiles/76561198073558458?time=1429340400 (April 18th)

http://backpack.tf/profiles/76561198073558458?time=1429599600 (April 21st)

This is an outlier. There's a current seller at 14 keys: http://www.tf2outpost.com/trade/26045139

Sale #2:

http://www.tf2outpost.com/trade/25971286

Sold for a Steaming Festivizer (13)

http://backpack.tf/profiles/76561198067895783?time=1432105200 (May 20th)

http://backpack.tf/profiles/76561198067895783?time=1432364400 (May 23rd)

http://www.tf2outpost.com/trade/25949426 No overpay since it was offered on the Festivizer.

13 keys

Sale #3:

http://www.tf2outpost.com/trade/25637070

Sold for 9 keys + 2 keys in metal ~11 keys

http://backpack.tf/profiles/76561198104074874?time=1428735600 (April 11th)

http://backpack.tf/profiles/76561198104074874?time=1428822000 (April 12th) - http://i.imgur.com/NMf9PSW.png

Sale #4:

Sold with a Blizz Noir for a Max

http://backpack.tf/profiles/76561198127551488?time=1431586800 (May 14th)

http://backpack.tf/profiles/76561198127551488?time=1431673200 (May 15th)

Likely a quicksell.