Just bought one of this.

Sale #1:

Bought mine for a Purple Energy Tough Guy's Toque:

http://m.imgur.com/3zFbJJQ

Proof of the effect of the Gatsby:

http://m.imgur.com/y37je3u

Proof of the effect of the Toque:

http://m.imgur.com/lgHH1E6

Total: 50*0.9 = 45 keys

Sale #2:

Sold for a Cloudy Moon Doctor's Sack, Collector's Mantreads and a Professional Killstreak Kukri:

http://www.tf2outpost.com/trade/26669934

Seller's backpack before: http://backpack.tf/profiles/76561198034367604?time=1438681700

Seller's backpack after: http://backpack.tf/profiles/76561198034367604?time=1438758000

Total: (48 + 2.6 + 3)*0.9 = ~48 keys

Mini Suggestion for the Cloudy Moon Doctor's Sack:

Sold for a Frostbite Gatsby:

http://www.tf2outpost.com/trade/26699143

The Gatsby trade:

http://www.tf2outpost.com/trade/26717985

Taking it as 48 keys, applying overpay later on

Mini Suggestion for the Strange Professional Killstreak Kukri:

It sells for around 3 keys on the SCM:

http://steamcommunity.com/market/listings/440/Strange%20Professional%20Killstreak%20Kukri

Please tell me if I did something wrong.