History 1: https://backpack.tf/item/9176718427

21 keys:

https://backpack.tf/profiles/76561198011321852#!/compare/1639785600/1639872000

https://backpack.tf/profiles/76561198941339786#!/compare/1638403200/1641772800

Hisotry 2: https://backpack.tf/item/9198689029

Untrace:

https://backpack.tf/profiles/76561198253093948#!/compare/1637366400/1637452800

https://backpack.tf/profiles/76561199000516657#!/compare/1636848000/1637452800

Buyout was 21 https://gladiator.tf/listings/6198cb59275431aff509c454

Since I already have a sale at 21 I'll put this suggestion up for now, but I'll ask for a screenshot just in case

Untrace:

https://backpack.tf/profiles/76561199000516657#!/compare/1641859200/1641945600

https://backpack.tf/profiles/76561198307613582#!/compare/1641600000/1641945600

https://backpack.tf/profiles/76561198307613582#!/compare/1642896000/1643068800

https://backpack.tf/profiles/76561198156475763#!/compare/1642982400/1643068800

22 keys match in buyer's side:

https://backpack.tf/profiles/76561198307613582#!/compare/1642896000/1643068800

https://backpack.tf/profiles/76561198156475763#!/compare/1642982400/1643068800

~~

https://marketplace.tf/items/tf2/31117;5;u16

$49.99 / $1.82 = 27.47 keys ~27 keys

taking 21-27 keys here

the first sale in history 2 was indeed 21 keys (credit to aj for the screenshot) https://imgur.com/pPfyhhF