Kinda surprised that this hasn't had any suggestions yet.

FIRST

Sold for a Circling Peace Sign Tartan Spartan(27 Keys)

http://backpack.tf/profiles/76561198132210093#!/compare/1488499200/1488585600

Sold for a Green Confetti Trophy Belt(23 Keys) and 1 Key(24 Keys total)

http://backpack.tf/profiles/76561198073829413#!/compare/1488412800/1488585600

http://backpack.tf/profiles/76561198114635132#!/compare/1488499200/1488585600

Sold for a Blizzardy Storm El Jefe(24 Keys) and 1 Key(25 Keys total)

http://backpack.tf/profiles/76561198171447795#!/compare/1488412800/1488499200

Quicksold for 22 Keys

http://backpack.tf/profiles/76561198048297608#!/compare/1488412800/1488499200

http://backpack.tf/item/5488601053

Sold for $28 in Marketplace

https://marketplace.tf/items/30069;5;u6

Low outlier

24-27.

Credits to Mindacos for finding the proof. All I did was make the actual suggestion.