Credit to Shuffle Spy

https://backpack.tf/item/4437828710

Sale 1) Sold for a Ventum Maris Citizen Cane

https://backpack.tf/profiles/76561198146552538#!/compare/1612569600/1612656000

Was already used there.

Sale 2) Sold for 60 Keys + 4 Unusuals

https://backpack.tf/profiles/76561198148511293#!/compare/1613088000/1613174400

https://gladiator.tf/listings/6027e82886383a33fcb85fc8 - Capped by the buyout of 87 Keys

Sale 3) Bulk sale

https://backpack.tf/profiles/76561198067194367#!/compare/1614988800/1615075200

Sale 4) Bulk sale

https://backpack.tf/profiles/76561198029656594#!/compare/1615680000/1615766400

Sale 5) Bulk sale

https://backpack.tf/profiles/76561198027338258#!/compare/1616716800/1616803200

https://backpack.tf/item/8049349496

Sale 6) Sold for 85 Keys + Airborne Enemies Killed (~2 Keys)

https://backpack.tf/profiles/76561197994697258#t9832848256

85 + 2 = 87 Keys

https://marketplace.tf/items/tf2/30748;5;u9 - Sold for $169.99 when Keys were ~$2.10 and $2.14 each

169.99 / 2.1 = 80.95, which rounds to 81 Keys

169.99 / 2.14 = 79.43, which rounds to 79 Keys