Sale 1:

Sold for 23 keys

http://www.tf2outpost.com/trade/26649347 (pretty quick, 3 days)

http://backpack.tf/profiles/76561198047860018?time=1438498800

http://backpack.tf/profiles/76561198047860018?time=1438585200

Sale 2:

Sold for a Stormy Storm Crocleather Slouch + a S.F. Flame Thrower

(21 + 13)*0.9 = 30.6 rounding to 31

http://backpack.tf/profiles/76561198066177907?time=1441522800

http://backpack.tf/profiles/76561198066177907?time=1441609200

Sale 3: (outlier)

Sold with a Pro S. Wrench for a Spec KS. Australium wrench

26 - 9 = 17 keys

http://backpack.tf/profiles/76561198051884476?time=1440831600

http://backpack.tf/profiles/76561198051884476?time=1441004400

Sale 4: (outlier, quicksell)

Quicksold for 25 keys

http://www.tf2outpost.com/trade/26748806

Sale 5: (outlier, quicksell)

Quicksold for 20??

http://backpack.tf/profiles/76561198083568872?time=1441004400

http://backpack.tf/profiles/76561198083568872?time=1442436018

Sale 6:

Sold for 27 keys + 4.2 in items

(4.2*0.9) + 27 = 30.78 rounding to 31 keys

http://backpack.tf/profiles/76561198047860018?time=1438412400

http://backpack.tf/profiles/76561198047860018?time=1438585200

Conclusion:

A lot of very quick sales at 25ish pure and 2 sales at 31. Taking 31.