Sale 1 :

Before : http://backpack.tf/profiles/76561198110226811?time=1446969600

After : http://backpack.tf/profiles/76561198110226811?time=1447056000

Sold for a Silver Cyclone Taunt: Deep Fried Desire : 19 * 0.9 = 17 keys

Sale 2 :

Before : http://backpack.tf/profiles/76561198030654668?time=1448006400

After : http://backpack.tf/profiles/76561198030654668?time=1448092800

Sold for a Circling TF Logo A Rather Festive Tree ( 22 ) but 1 key in items was added : 22 - 1 = 21 keys

Mini on the festive tree :

Before : http://backpack.tf/profiles/76561198240514618?time=1447833600

After : http://backpack.tf/profiles/76561198240514618?time=1447920000

Sold for a Disco Beat Down Desert Marauder : 24 * 0.9 = 22 keys

Only recent sales taking the range of 17-21 keys.

Supportive criticism welcome