Sale 1:

Sold for 11 keys

Seller: https://backpack.tf/profiles/76561198061533354#!/compare/1549584000/1549670400

Buyer: https://backpack.tf/profiles/76561198097861115#!/compare/1549584000/1549670400

https://backpack.tf/item/172206202

X = 11

Sale 2:

Sold to a bot for 10 keys

Seller: https://backpack.tf/profiles/76561198072513910#!/compare/1510444800/1548201600

Buyer: https://backpack.tf/profiles/76561198315588518#!/compare/1548201600/1553040000

https://backpack.tf/item/3708683595

https://i.imgur.com/P1Eqy41.png - bot.tf confirms

X = 10

Marketplace Sales:

https://marketplace.tf/items/151;5;u7

https://manic.tf/keyprice/?at=2019-01-22 - $22.61 / $1.75 = 12.92 keys

$16 went to a buy order, excluding.

X = 13

Other Sales:

https://backpack.tf/item/172206202 (#1)

https://backpack.tf/item/144903288 (#2, excluded gambling)

https://backpack.tf/item/272486230 - marketplace

https://backpack.tf/item/177867154 - marketplace

#1

Bulk for Green Energy Pyromancer’s Mask

https://backpack.tf/profiles/76561198086747482#!/compare/1549497600/1549584000

https://backpack.tf/profiles/76561198061533354#!/compare/1549497600/1549584000

#2

Sold for 9 keys?

https://backpack.tf/profiles/76561198841365001#!/compare/1548028800/1548115200

https://backpack.tf/profiles/76561198157089186#!/compare/1548201600/1548288000

Hard to tell as the buyer bought another hat from the seller on the same day.

Sellers:

https://i.imgur.com/ER7HNyo.png

https://backpack.tf/item/144903288 - ~10.2 keys

https://backpack.tf/item/3708683595 - 11 keys

Sales at:

10

11

13

13 is too high give current sellers. Excluding 13.

Going with 10-11.