Sale 1:

Sold for 9 keys

https://backpack.tf/profiles/76561198850121720#!/compare/1706745600/1706832000

https://backpack.tf/profiles/76561198045674946#!/compare/1706832000/1706918400

https://backpack.tf/item/4260949921

= 9 keys

Sale 2:

Sold for 7 keys + ~1 key in metal

https://backpack.tf/profiles/76561198850121720#!/compare/1706572800/1706659200

https://backpack.tf/profiles/76561198136744617#!/compare/1706486400/1706659200

https://backpack.tf/item/4302882915

= 8 keys

Sale 3:

Sold for 7 keys + 59.22 ref

https://backpack.tf/profiles/76561199139085248#!/compare/1704412800/1704499200

https://backpack.tf/profiles/76561198289262589#!/compare/1704326400/1704931200

https://gladiator.tf/sales?item=Holy%20Grail%20Taunt:%20Zoomin%27%20Broom&at=2024-01-07T07:56:28.397Z - gladiator confirms

https://backpack.tf/item/4258389669

= 8 keys

Sale 4:

Sold for 7 keys

https://backpack.tf/profiles/76561198963406131#!/compare/1702771200/1702857600

https://backpack.tf/profiles/76561198117597416#!/compare/1702771200/1702857600

https://backpack.tf/item/4376753839

= 7 keys

Sale 5:

Sold for 7 keys

https://backpack.tf/profiles/76561198320464891#!/compare/1703980800/1704326400

https://backpack.tf/profiles/76561198258378121#!/compare/1703894400/1704326400

https://backpack.tf/item/4376753839

= 7 keys

Sale 6:

Sold for 7 keys

https://backpack.tf/profiles/76561198850121720#!/compare/1703116800/1703203200

https://backpack.tf/profiles/76561199034260371#!/compare/1702944000/1703721600

https://backpack.tf/item/4302882915

= 7 keys

Other Sales:

#1

https://backpack.tf/profiles/76561198086767799#!/compare/1705017600/1705363200

https://backpack.tf/profiles/76561199521837458#!/compare/1705190400/1705276800

https://backpack.tf/item/10929279095

Bulk/backpack buy

#2

https://backpack.tf/profiles/76561199521837458#!/compare/1705276800/1705363200

https://backpack.tf/profiles/76561198841279602#!/compare/1705276800/1705363200

https://backpack.tf/item/10929279095

Untraceable

#3

https://backpack.tf/profiles/76561198311498888#!/compare/1703116800/1703203200

https://backpack.tf/profiles/76561199560836533#!/compare/1702944000/1703203200

https://backpack.tf/item/10282876845

Untraceable. 7 keys + some metal match, would've been more.

#4

https://backpack.tf/profiles/76561199560836533#!/compare/1703462400/1703808000

https://backpack.tf/profiles/76561198453530349#!/compare/1703635200/1703721600

https://backpack.tf/item/10282876845

Untraceable

#5

https://backpack.tf/profiles/76561198453530349#!/compare/1703980800/1704067200

https://backpack.tf/profiles/76561198157279796#!/compare/1703980800/1704240000

https://backpack.tf/item/10282876845

Untraceable

#6

https://backpack.tf/profiles/76561199081943572#!/compare/1703462400/1703548800

https://backpack.tf/profiles/76561198850178158#!/compare/1703462400/1703548800

https://backpack.tf/item/8119545713

Untraceable. ~2.5 keys match. Gambled prior.

#7

https://backpack.tf/profiles/76561198097961584#!/compare/1702598400/1702771200

https://backpack.tf/profiles/76561199132184792#!/compare/1702512000/1702598400

https://gladiator.tf/sales?item=Holy%20Grail%20Taunt:%20Zoomin%27%20Broom&at=2023-12-16T07:35:45.758Z - labelled as 6 keys + 31.77 ref

https://backpack.tf/item/6080490613

Untraceable

#8

https://backpack.tf/profiles/76561198117597416#!/compare/1703030400/1703116800

https://backpack.tf/profiles/76561198320464891#!/compare/1703376000/1703721600

https://backpack.tf/item/4376753839

Most likely the marketplace sale:

https://marketplace.tf/items/tf2/30672;5;u3003

#9

https://backpack.tf/profiles/76561198080979276#!/compare/1702598400/1703030400

https://backpack.tf/profiles/76561198850121720#!/compare/1702512000/1702598400

https://backpack.tf/item/4302882915

Untraceable. Some cosmetics/taunts match.

#10

https://backpack.tf/profiles/76561199034260371#!/compare/1705190400/1707264000

https://backpack.tf/profiles/76561198850121720#!/compare/1705622400/1705708800

https://backpack.tf/item/4302882915

Untraceable

#11

https://backpack.tf/profiles/76561198069881436#!/compare/1703548800/1703894400

https://backpack.tf/profiles/76561198211858204#!/compare/1703721600/1703894400

https://backpack.tf/item/4263813380

Backpack buy/alt transfer or something

#12

https://backpack.tf/profiles/76561198137924934#!/compare/1706140800/1706227200

https://backpack.tf/profiles/76561199110809353#!/compare/1706140800/1706227200

https://backpack.tf/item/4260949921

Bulk for keys

https://backpack.tf/item/5425169738 - mannco

https://backpack.tf/item/4260585762 - gambled

Marketplace Sales:

https://marketplace.tf/items/tf2/30672;5;u3003

$16.99, December 26th

https://marketplace.tf/items/tf2/5021;6

Keys were $1.72 on December 26th

16.99/1.72 = ~9.9 keys

= 10 keys

Sellers:

https://imgur.com/a/npQvmkD

https://backpack.tf/item/4376753839 - 10 keys

https://backpack.tf/item/4263813380 - 14 keys

https://backpack.tf/item/6134236989 - marketplace

https://backpack.tf/item/4427907971 - marketplace

https://backpack.tf/item/6080490613 - marketplace

Sales at:

7 (3x)

8 (2x)

9

10 (marketplace)

Many buyers at 7 keys, excluding 7.

Taking 8-10 keys.