2 of my suggestions conflict with each others, have to close one :(

Hate it when that happens.

Sale 1

http://www.tf2outpost.com/trade/21688916 - Sold for Orbiting Fire Hound Dog (Outdated, mini below), he added 1 key, no overpay's needed = 18 - 1 = 17 keys

Mini for Orbiting Fire Hound Dog:

http://www.tf2outpost.com/trade/21240481 - Sold for 18 keys

Sale 2

http://www.tf2outpost.com/trade/21100637 - Sold for 14 keys

Sale 3

http://www.tf2outpost.com/trade/21617378 - Sold for Bubbling Gym Rat (Outdated, mini below) + 3 keys + 4 keys in items = 17*0.9 + 4 = 18 keys (Outlier)

Mini for Bubbling Gym Rat

http://www.tf2outpost.com/trade/21421013 - 10 keys + 3 keys in items = 13 keys

Sale 4

http://www.tf2outpost.com/trade/21557993 - Sold for Screaming Tiger Battin' a Thousand which he later sold for 5.3 buds? (Outlier)

Sale 5

http://www.tf2outpost.com/trade/21243956 - Sold for 15 keys

Sale 6

http://www.tf2outpost.com/trade/21180360 - Traded for Disco Beat Down Front Runner (6 buds), he added 1 bud => 5 buds (Outlier)

Sale 7

http://www.tf2outpost.com/trade/21285149 - Sold for a Bill's Hat + 13 keys worth in items (13*0.9 = 12 keys) = 18 keys (Outlier)

Sellers

http://www.tf2outpost.com/trade/21616259 - 15 keys

http://www.tf2outpost.com/trade/21750654 - 16.5 keys

http://www.tf2outpost.com/trade/21649749 - 1 bud

http://www.tf2outpost.com/trade/21186037 - 18 keys (Unsold for 3 weeks, have 15 keys offer)

Feel free to counter / support my proofs.