Sale 1 : http://www.tf2outpost.com/trade/26599809

Before : http://backpack.tf/profiles/76561198128032188?time=1437980400

After : http://backpack.tf/profiles/76561198128032188?time=1438066800

Sold for a Cloud 9 Troublemaker's Tossle Cap : 47 * 0.9 = 42 keys

Sale 2 :

Before : http://backpack.tf/profiles/76561198072573105?time=1439362800

After : http://backpack.tf/profiles/76561198072573105?time=1439708400

Sold for a duped Phosphorous Stout Shako : 40 keys

Mini on the duped shako :

Before : http://backpack.tf/profiles/76561198072573105?time=1439708400

After : http://backpack.tf/profiles/76561198072573105?time=1440226800

Sold for a Terror-Watt Whoopee Cap ( 20 ) + a Dead Presidents Bonk Boy ( 24 ) : 44 * 0.9 = 40 keys

Sale 3 :

Before : http://backpack.tf/profiles/76561198085880346?time=1437721200

After : http://backpack.tf/profiles/76561198085880346?time=1437894000

Sold for a Phosphorous Medic's Mountain Cap ( 30 ) + 1 key in items : 41 * 0.9 = 37 keys

Thus taking the range of 37 to 42 keys.

Supportive criticism welcome