well counter i guess.

sale 1: sold with nuts helmet[9 keys via mini] without a home for sulph bot dogger[33 keys]

http://www.tf2outpost.com/trade/26095059

33*0.9=29.7 rounding to 30

30-9=21

mini on hwah: b/o of 9 keys

http://www.tf2outpost.com/trade/26001199

sale 2: sold for a max[26 keys at time of sale?]

http://www.tf2outpost.com/trade/25920287

sale 3: sold for stormy dragonborn[30.5 keys]

http://backpack.tf/profiles/76561198065573877?time=1430809200

http://backpack.tf/profiles/76561198065573877?time=1430895600

30.5*0.9=27.45 rounding down to 27

sale 4: sold for planets bone[13 keys]

http://backpack.tf/profiles/76561198120180998?time=1429945200

http://backpack.tf/profiles/76561198120180998?time=1430031600

13*0.9=11.7 rounding to 12

credits to kevin for sale 1, 2, and 3.

credits to ḎℰѦÐ! бум for sale 4.

so sales at 12, 21, 26, and 27, and a sale at 9 on the other suggestion.

3 sales at 20+, 2 sales at lower than 15, calling 9 and 12 outliers.

taking a final price of 21-27.