Sale 1:

Sold for Vintage Bill's Hat (1.5) = 1.5

http://www.tf2outpost.com/trade/20831526

http://backpack.tf/profiles/76561198084815409?time=1405115141 → http://backpack.tf/profiles/76561198128284342?time=1405062000

Sale 2: (invalid sale, outdated price)

Sold for Stormy Hot Dogger (1.25*0.9) + Flies Mullet (~0.68) = 1.125 + 0.62 = 1.745 (rounding to 1.6, B/O was 30 keys)

http://www.tf2outpost.com/trade/21159084

http://backpack.tf/profiles/76561198066065032?time=1405580400 → http://backpack.tf/profiles/76561198066065032?time=1405666800

Sale 3:

Cannot identify what it sold for

http://www.tf2outpost.com/trade/22349892

Sale 4:

Sold for Strange Machina ([18/18.5]*0.9) + 7 keys ([7/18.5]) = 0.88 + 0.38 = 1.26 (rounding to 1.3)

http://www.tf2outpost.com/trade/22036097

http://backpack.tf/profiles/76561198037947164?time=1409122800 → http://backpack.tf/profiles/76561198037947164?time=1409382000

Sale 5:

Sold for 27 keys ([27/18.5]) = 1.46 (rounding to 1.5)

http://www.tf2outpost.com/trade/22358432

http://backpack.tf/profiles/76561198097567844?time=1409382000 → http://backpack.tf/profiles/76561198097567844?time=1409525972

Notes:

http://www.tf2outpost.com/trade/20718828 - B/O 28 keys (~1.5)

http://www.tf2outpost.com/trade/22126138 - B/O 1 bud 10 keys (~1.5)

http://www.tf2outpost.com/trade/22251960 - B/O 1.5

Feel free to support/counter my suggestion!