Sale 1: (complex, outlier)

Sold a Strange It's A Secret To Everybody Private Eye for a Green Confetti Team Captain and 41 keys

(100*0.9) + 41 - 87.5 = 43.5

Calling it an outlier based on the seller and the fact that this is a complex sale

http://www.tf2outpost.com/trade/25987173 B/O of 65

http://backpack.tf/profiles/76561198071371521?time=1432191600 (May 21st)

http://backpack.tf/profiles/76561198071371521?time=1432278000 (May 22nd)

Sale 2: (outlier)

Sold for Cauldron Bubbles Tyrant's Helm, a Strange Festive Buff Banner and 5 keys

(61 + 2)*0.9 + 5 = 61.7 rounding to 62 keys

http://www.tf2outpost.com/trade/23824847

http://backpack.tf/profiles/76561198008114236?time=1430118000 (April 27th)

http://backpack.tf/profiles/76561198008114236?time=1430377200 (April 30th)

Sale 3:

Sold with 17 keys for a Molten Mallard Executioner

(181*0.9) - 17 = 145.9 capping at 90 keys

http://www.tf2outpost.com/trade/26015055 Had a B/O of 90, can be proven by my last suggestion: http://backpack.tf/vote/id/5560b930b98d8875448b4616

http://backpack.tf/profiles/76561198071371521?time=1432450800 (May 24th)

http://backpack.tf/profiles/76561198071371521?time=1432537200 (May 25th)

Sale 4:

Sold for a Burning Cock ;)

(87.5*0.9) = 78.75 rounding to 79 keys

http://www.tf2outpost.com/trade/26102154

http://i.imgur.com/6JwlgJv.png

Notes:

Mini for the Burning Cock ;): ~87.5

http://backpack.tf/vote/id/556e7be9ba8d88de088b4578

Mini for the Green Confetti Team Captain:

Sold for a Scorching Noble

(126.5*0.9) = 113.85 caps at 100 keys

http://www.tf2outpost.com/trade/25975581

http://backpack.tf/profiles/76561198122631490?time=1432018800 (May 19th)

http://backpack.tf/profiles/76561198122631490?time=1432191600 (May 21st)

Mini for the Cauldron Bubbles Tyrant's Helm:

http://backpack.tf/vote/id/5560b387dea9e932318b4615

Conclusion:

Taking the final range at 80 to 90 keys.