Is there a theme I'm missing here?

Sale 1:

Sold for 30 keys

http://www.tf2outpost.com/trade/27092880

http://backpack.tf/profiles/76561198045458826?time=1444806000&compare=1443164400 (Buyer)

http://backpack.tf/profiles/76561198090956917?time=1443078000&compare=1443250800 (Seller)

X = 30

Sale 2:

Sold for 15 keys

http://www.tf2outpost.com/trade/27329152

http://backpack.tf/profiles/76561198008808867?time=1448438400&compare=1448611200 (Seller)

http://backpack.tf/profiles/76561198087833652?time=1448611200&compare=1448524800 (Buyer)

X = 15

Sale 3:

Sold for 33 keys

http://www.tf2outpost.com/trade/27500764 - "Quickselling, 40 keys pure!"

http://backpack.tf/profiles/76561198087833652?time=1449216000&compare=1449302400 (Seller)

Buyer's backpack history during the sale was ~2 months apart

X = 33

Sale 4:

Sold for Purple Energy Bombing Run

No outpost link available

http://backpack.tf/profiles/76561198217482852?time=1448092800&compare=1448006400 (Seller)

http://backpack.tf/profiles/76561198108063138?time=1448006400&compare=1448092800 (Buyer)

X = 28.5*0.9

X = 26

Sale 5:

Sold with a key, 2.5 keys in items and 0.88 ref for Morning Glory Rimmed Raincatcher

http://www.tf2outpost.com/trade/27501750

http://backpack.tf/profiles/76561198108063138?time=1448611200&compare=1448697600 (Seller)

http://backpack.tf/profiles/76561198177092939?time=1448697600&compare=1448611200 (Buyer)

I'd assume the Trilby was offered, because he added those items to the trade, therefore, no overpay.

X + 3.5 = 35

X = 31.5

Rounding to 32

Sale 6:

Sold with Taunt: Zoomin' Broom for Orbiting Planets Vive la France

http://www.tf2outpost.com/trade/27509399

http://backpack.tf/profiles/76561198177092939?time=1448784000&compare=1449043200 (Seller)

http://backpack.tf/profiles/76561198158459733?time=1448956800&compare=1449043200 (Buyer)

Same deal with Sale 5 - no overpay

X + 2.5 = 36

X = 33.5

Rounding to 34

Sale 7: Not using

Bulk for Death at Dusk Prancer's Pride

http://www.tf2outpost.com/trade/27537489

http://backpack.tf/profiles/76561198158459733?time=1449216000&compare=1449129600 (Seller)

http://backpack.tf/profiles/76561198065929810?time=1449216000&compare=1448956800 (Buyer)

Sale 8:

Sold with 2 keys for Cloud 9 Grenadier's Softcap + 5 keys in soldier stuff

http://www.tf2outpost.com/trade/27538712

http://backpack.tf/profiles/76561198065929810?time=1449216000&compare=1449302400 (Seller)

http://backpack.tf/profiles/76561198084752432?time=1449302400&compare=1449216000 (Buyer)

X + 2 = (26 + 5)0.9

X + 2 = 28

X = 26

Mini on Softcap:

Sold for 26 keys

http://www.tf2outpost.com/trade/27166388

http://backpack.tf/profiles/76561197973248859?time=1443682800&compare=1443942000

There's also an unsold at 3 months on the classifieds for 30 keys

Sales at:

15 - outlier

26

26

30

32

33

34

Going with 26-34, I guess