Resuggestion: https://backpack.tf/suggestion/5dc5e63ed3817231400b4677

Sale 1-3:

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

$8.05 / $1.83 = 4.40 keys

$16.83 / $1.80 = 9.35 keys

$8.2 / $1.78 = 4.61 keys

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:

6.5 keys

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

Sale 14:

bulk

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

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

Sale 15:

BP purchase

https://backpack.tf/profiles/76561198045245128#!/compare/1573516800/1573776000

https://backpack.tf/profiles/76561198084367252#!/compare/1573689600/1573776000

Sale 16:

untrace

https://backpack.tf/profiles/76561198161748319#!/compare/1575936000/1576022400

https://backpack.tf/profiles/76561198077721723#!/compare/1575504000/1576022400

Sale 17:

Sold with nether lounge, buyers on lounge at 10 keys makes this bulk

https://backpack.tf/profiles/76561198134509644#!/compare/1574726400/1574812800

https://backpack.tf/profiles/76561198071498662#!/compare/1574726400/1574812800

Sale 18:

3 keys

https://backpack.tf/profiles/76561198203987639#!/compare/1573430400/1573862400

https://backpack.tf/profiles/76561198871755761#!/compare/1573776000/1574121600

Sale 19:

untrace

https://backpack.tf/profiles/76561198072465460#!/compare/1574726400/1575072000

https://backpack.tf/profiles/76561198871755761#!/compare/1574726400/1574899200

Sale 20:

untrace, likely buy order

https://backpack.tf/profiles/76561198834188334#!/compare/1573862400/1573948800

https://backpack.tf/profiles/76561198838447026#!/compare/1573776000/1573862400

Sale 21:

3 keys + 11 or 12 ref

https://backpack.tf/profiles/76561198838447026#!/compare/1573948800/1574035200

https://backpack.tf/profiles/76561198210225228#!/compare/1573948800/1574035200

Sale 22:

untrace

https://backpack.tf/profiles/76561198164772319#!/compare/1572566400/1573689600

https://backpack.tf/profiles/76561198856405336#!/compare/1573171200/1574035200

Sale 23:

2 keys + 36 ref ( buy order: https://imgur.com/a/vB0F6ir )

https://backpack.tf/profiles/76561198811155197#!/compare/1572912000/1573516800

https://backpack.tf/profiles/76561198363395191#!/compare/1573430400/1573516800

Sale 24:

untrace, possibly SCM

https://backpack.tf/profiles/76561198363395191#!/compare/1573689600/1573776000

https://backpack.tf/profiles/76561198044479067#!/compare/1573516800/1574121600

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

Sales:

3, 3.2, 4.5, 4.6, 6.5, 9.5

1 month unsold at 5 keys: https://imgur.com/a/u5BxBIJ