Sale 1 :

Before : http://backpack.tf/profiles/76561197996907270?time=1441522800

After : http://backpack.tf/profiles/76561197996907270?time=1441954800

Sold for 22 keys.

Sale 2 :

Before : http://backpack.tf/profiles/76561197963746116?time=1442300400

After : http://backpack.tf/profiles/76561197963746116?time=1442386800

Sold for a pro ks grenade launcher : 28 * 0.9 = 25 keys

Sale 3 :

Before : http://backpack.tf/profiles/76561198079275897?time=1439190000

After : http://backpack.tf/profiles/76561198079275897?time=1439276400

Sold for a Green Energy Pyro's Beanie ( 23 ) + 5 keys in items : 28 * 0.9 = 25 keys

Sale 4 :

Before : http://backpack.tf/profiles/76561198054795373?time=1443078000

After : http://backpack.tf/profiles/76561198054795373?time=1443942000

Sold for a pro ks aussie flam thrower : 25 * 0.9 = 23 keys

Taking the range of 22-25 keys.

Supportive criticism welcome