Sale 1-2:

https://marketplace.tf/items/tf2/1109;5;u3030

$8.05 / $1.83 = 4.40 keys

$16.83 / $1.80 = 9.35 keys

Sale 3:

bulk

https://backpack.tf/profiles/76561198161748319#!/compare/1572998400/1573084800

https://backpack.tf/profiles/76561197995378859#!/compare/1572393600/1572998400

Sale 4:

crafted, not a sale

https://backpack.tf/profiles/76561198071498662#!/compare/1569456000/1572048000

Sale 5:

Bulk

sold with 22 keys for Ghastly Ghosts Soldier's Requiem

https://backpack.tf/profiles/76561197994697258#!/compare/1572393600/1572480000

https://backpack.tf/profiles/76561198102868313#!/compare/1572307200/1572480000

Sale 6:

crafted, not a sale

https://backpack.tf/profiles/76561198061398890#!/compare/1571443200/1572134400

Sale 7:

crafted, not a sale

https://backpack.tf/profiles/76561198868286835#!/compare/1571875200/1571961600

Sale 8:

Bulk for Enchanted Kazotsky Kick

https://backpack.tf/profiles/76561198025083656#!/compare/1572220800/1572307200

https://backpack.tf/profiles/76561198146200909#!/compare/1572220800/1572307200

Sale 9:

crafted, not a sale

https://backpack.tf/profiles/76561198807658771#!/compare/1568678400/1572048000

Sale 10:

Bulk

https://backpack.tf/profiles/76561198827261786#!/compare/1572912000/1572998400

https://backpack.tf/profiles/76561198384385308#!/compare/1572912000/1573084800

Sale 11:

untrace

https://backpack.tf/profiles/76561198313773136#!/compare/1572652800/1572739200

https://backpack.tf/profiles/76561198196394830#!/compare/1572652800/1572739200

Sale 12:

Sold with 2 keys for KaW Employee of the Mmmph(8.5 keys)

https://backpack.tf/profiles/76561198313773136#!/compare/1572739200/1572825600

https://backpack.tf/profiles/76561198200309337#!/compare/1572739200/1572825600

Employee: https://backpack.tf/suggestion/5dc5e5a4d3817232bc437714

Sale 13:

untrace

https://backpack.tf/profiles/76561198823526388#!/compare/1572825600/1572912000

https://backpack.tf/profiles/76561198200309337#!/compare/1572739200/1572825600

=======================================================================

Sales:

4.5, 8.5, 9.5