Counter-suggestion

Sale 1

http://www.tf2outpost.com/trade/22791391 - Sold for an Orbiting Fire Stately Steel Toe (14*0.9 = 13 keys)

Mini for the Orbiting Fire Stately Steel Toe:

http://backpack.tf/vote/id/542e7490b88d8880258b4c43

Sale #2

Sold for planets grimm (1.2 buds (20 keys) * 0.9 = 18 keys)

No notable sweets (I may have missed a craft hat or something) were added. Check the backpack history links if you want.

http://www.tf2outpost.com/trade/22787607 > http://www.tf2outpost.com/trade/22791391

Sellers backpack:

http://backpack.tf/profiles/76561198116218395?time=1411282800 >

http://backpack.tf/profiles/76561198116218395?time=1411455600

Mini for the Planets Grimm:

http://backpack.tf/vote/id/542eb7b5b98d8829268b45e2

Sale 3

http://www.tf2outpost.com/trade/22833132 - Sold to a quick-buyer for a TS Bill (6 keys) + 4 keys = 10 keys

Had a b/o of 15 keys

Sale #4

http://www.tf2outpost.com/trade/22680324

http://backpack.tf/profiles/76561198111430606?time=1411023600 >

http://backpack.tf/profiles/76561198111430606?time=1411110000

Sold for a bliz Brigade Helm

17 keys * 0.9 = 15 keys

I'm not sure what's up with all that ref entering his backpack, but it doesnt seem to have anything to do with the sale

Given the b/o at 15 keys, and the sales at 15 and 13, it’s safe to call 18 an outlier, and use 13 -15 as the value