Marketplace Sales:

https://marketplace.tf/items/tf2/31321;5;u3003

$8.99 on December 13th and January 14th

https://backpack.tf/item/12429462533 - Jan 14th

Snapshots don't go far back enough to look for a B/O.

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

Keys were:

1.75, December 13th (looks like a small spike in the graph, using 1.73 instead)

1.68, Jan 14th

8.99/1.75 = ~5.15, rounds to 5 keys

8.99/1.68 = ~5.35, rounds to 5.5 keys

Other Sales:

#1

https://backpack.tf/profiles/76561198191933566#!/compare/1703116800/1703289600

https://backpack.tf/profiles/76561199564942025#!/compare/1703116800/1703203200

https://backpack.tf/item/12547284740

Untraceable

#2

https://backpack.tf/profiles/76561199564942025#!/compare/1706313600/1706400000

https://backpack.tf/profiles/76561198422066161#!/compare/1706400000/1706486400

https://backpack.tf/item/12547284740

Untraceable. 4 keys match, I'm certain more were involved.

https://backpack.tf/item/12937386952 - mannco

#3

https://backpack.tf/profiles/76561198422066161#!/compare/1706745600/1706832000

https://backpack.tf/profiles/76561198882175555#!/compare/1706400000/1706918400

https://backpack.tf/item/12547284740

Bulk for Starlight Sophisticated Smoker

#4

https://backpack.tf/profiles/76561198845931844#!/compare/1702598400/1703289600

https://backpack.tf/profiles/76561199522145204#!/compare/1703203200/1703289600

https://backpack.tf/item/12429462533

Backpack buy

#5

https://backpack.tf/profiles/76561199522145204#!/compare/1703203200/1703289600

https://backpack.tf/profiles/76561197982127154#!/compare/1703203200/1703289600

https://backpack.tf/item/12429462533

Probably another backpack buy

https://backpack.tf/item/13176556625 - wasn't unusual

Sellers:

https://imgur.com/a/C4aaYdc

https://backpack.tf/item/13565059523 - ~5.5 keys

https://backpack.tf/item/14118668154 - 6 keys

Sales at:

5 (marketplace)

5.5 (marketplace)

Taking 5-5.5.