Starmie(t)

https://backpack.tf/item/5206412333

Sale 1) Sold for a Duped Orbiting Fire Gentleman's Ushanka (22 Keys) + 1 Key + 0.5 Keys of Refined at the time

https://backpack.tf/profiles/76561198087540393#!/compare/1500076800/1500422400

22 + 1 + 0.5 = 23.5, which rounds to 24 Keys

http://www.tf2outpost.com/trade/29226358 - The Buyout was 24 Keys

https://backpack.tf/item/5215511551

Sale 2) Sold + 4 Keys for a Disco Beat Down Officer's Ushanka (27.5 Keys)

https://backpack.tf/profiles/76561198067007358#!/compare/1499558400/1499644800

27.5 - 4 = 23.5, which rounds to 24 Keys

Ushanka Mini

https://backpack.tf/suggestion/599d6c14cf6c753e7c50bad7 - 27.5 Keys

Sale 3) Sold for a Strange Vivid Plasma Airdog + Specialized Killstreak Collector's Tomislav

https://backpack.tf/profiles/76561198343505253#!/compare/1499558400/1499644800

http://www.tf2outpost.com/trade/29268389 - Capped by the Buyout of 22 Keys

https://backpack.tf/item/5189877987

Sale 4) Sold either for 18 Keys or a Max's Severed Head

https://backpack.tf/profiles/76561198126979379#!/compare/1501718400/1501804800 - Buyer's Backpack

https://backpack.tf/profiles/76561198213764372#!/compare/1501804800/1501891200 - Seller's Backpack

Either way, this sale is a low Outlier.