4 in the world.

Sale 1 : (outlier)

Before : http://backpack.tf/profiles/76561198072803119?time=1431013379

After : http://backpack.tf/profiles/76561198072803119?time=1431068400

Sold for a Dead Presidents Killer's Kabuto : 30 keys * 0.9 = 27 keys

Sale 2 :

Before : http://backpack.tf/profiles/76561197976252454?time=1430290800

After : http://backpack.tf/profiles/76561197976252454?time=1430390319

Sold for a gifted Nuts n' Bolts Modest Metal Pile of Scrap ( 20 keys ) + 1 key in items : 21 * 0.9 = 19 keys

Mini on the gifted pile of scrap :

Before : http://backpack.tf/profiles/76561198153961098?time=1429772400

After : http://backpack.tf/profiles/76561198153961098?time=1429864564

Sold for a Stormy Storm Noble Amassment of Hats : 22 * 0.9 = 20 keys

Sale 3 :

Before : http://backpack.tf/profiles/76561198048522579?time=1426230000

After : http://backpack.tf/profiles/76561198048522579?time=1426362122

Sold for an aussie grenade launcher = 18 keys

Thus taking a range of 18 to 19 keys.

Suportive criticism welcome