Last 3 months looked into.

The Sale:

Sold for 2 keys + 16 ref

https://backpack.tf/profiles/76561198890990852#!/compare/1702425600/1702512000

https://backpack.tf/profiles/76561199466655104#!/compare/1702339200/1702512000

https://backpack.tf/item/8828977161

= 2.25 keys

Other Sales:

#1

https://backpack.tf/profiles/76561199101483088#!/compare/1702944000/1703030400

https://backpack.tf/profiles/76561198218791111#!/compare/1702944000/1703030400

https://backpack.tf/item/13371296918

https://gladiator.tf/sales?item=Holy%20Grail%20Taunt:%20The%20Headcase&at=2023-12-20T09:37:47.830Z - labelled as 1 key + 52.55 ref

Untraceable

#2

https://backpack.tf/profiles/76561198218791111#!/compare/1702944000/1703030400

https://backpack.tf/profiles/76561199132184792#!/compare/1702944000/1703030400

https://backpack.tf/item/13371296918

Untraceable

#3

https://backpack.tf/profiles/76561199132184792#!/compare/1703030400/1703116800

https://backpack.tf/profiles/76561198409084388#!/compare/1675209600/1705017600

https://backpack.tf/item/13371296918

Untraceable

#4

https://backpack.tf/profiles/76561199394463680#!/compare/1703462400/1703808000

https://backpack.tf/profiles/76561199110809353#!/compare/1703376000/1703462400

https://backpack.tf/item/12415682784

Bulk/untraceable

#5

https://backpack.tf/profiles/76561199161845450#!/compare/1702771200/1704412800 (won't update)

https://backpack.tf/profiles/76561199059800460#!/compare/1704326400/1704412800

https://backpack.tf/item/11198990794

Untraceable

#6

https://backpack.tf/profiles/76561198997567309#!/compare/1699920000/1701907200 (won't update)

https://backpack.tf/profiles/76561198306870587#!/compare/1702512000/1702598400

https://backpack.tf/item/11042414192

Untraceable

#7

https://backpack.tf/profiles/76561199466655104#!/compare/1703203200/1703289600

https://backpack.tf/profiles/76561199564942025#!/compare/1703203200/1703289600

https://backpack.tf/item/8828977161

Untraceable

#8

https://backpack.tf/profiles/76561199564942025#!/compare/1703376000/1703462400

https://backpack.tf/profiles/76561198121842482#!/compare/1703462400/1703721600

https://backpack.tf/item/8828977161

Untraceable. Probably bulk, considering the amount of keys that match on the buyer's end.

The rest of the item's history involves scammers or gambling.

#9

https://backpack.tf/profiles/76561199106461781#!/compare/1704153600/1704499200

https://backpack.tf/profiles/76561198850274253#!/compare/1704412800/1704499200

https://backpack.tf/item/8342024682

Bulk for keys

#10

https://backpack.tf/profiles/76561198275154229#!/compare/1702512000/1702771200

https://backpack.tf/profiles/76561198890990852#!/compare/1702598400/1702684800

https://backpack.tf/item/8044393319

Untraceable. 1 key + a small amount of metal match.

#11

https://backpack.tf/profiles/76561199446547741#!/compare/1705536000/1706918400

https://backpack.tf/profiles/76561198135388328#!/compare/1706486400/1706572800

https://backpack.tf/item/6719942716

Untraceable

#12

https://backpack.tf/profiles/76561198135388328#!/compare/1706486400/1706572800

https://backpack.tf/profiles/76561199026390261#!/compare/1706486400/1706572800

https://backpack.tf/item/6719942716

Untraceable. Would've been flipped between bots for profit without being scanned in their backpack.

#13

https://backpack.tf/profiles/76561199061291714#!/compare/1707091200/1707177600

https://backpack.tf/profiles/76561199315621199#!/compare/1707177600/1707264000

https://backpack.tf/item/8828977161

Untraceable/Bulk

#14

https://backpack.tf/profiles/76561199026390261#!/compare/1707696000/1707782400

https://backpack.tf/profiles/76561199010300186#!/compare/1707782400/1707782400

https://backpack.tf/item/6719942716

Untraceable

#15

https://backpack.tf/profiles/76561199519596103#!/compare/1701648000/1708300800

https://backpack.tf/profiles/76561199026390261#!/compare/1708214400/1708300800

https://backpack.tf/item/12909394210

Untraceable

#16

https://backpack.tf/profiles/76561199026390261#!/compare/1708992000/1709078400

https://backpack.tf/profiles/76561199017959799#!/compare/1708992000/1709078400

https://backpack.tf/item/12909394210

Untraceable. Gambled afterwards.

https://backpack.tf/item/8408682470 - mannco

Sellers:

https://imgur.com/a/jIT5nDY

https://backpack.tf/item/11198990794 - 3 keys

https://backpack.tf/item/6258215032 - 3 keys

https://backpack.tf/item/7108321203 - marketplace

https://backpack.tf/item/6252989012 - marketplace

1 sale at 2.25 keys.

https://marketplace.tf/items/tf2/30876;5;u3003

4 sales at/over $6 on marketplace, which will end up being around 3.5 keys at the lowest. Considering the 2 sellers at 3 keys, these sales will have to be excluded.

Taking 2.25 keys flat.

https://backpack.tf/profiles/76561198009027213#!/compare/1710374400/1710460800

https://backpack.tf/profiles/76561197995896476#!/compare/1397631600/1710892800

https://backpack.tf/item/6255196618

Untraceable, probably scammed/alt transfer