Sale 1:

Sold for Spec. KS Factory New Current Event Scattergun (~7) + 3 keys

Seller: https://backpack.tf/profiles/76561198849487866#!/compare/1550275200/1550361600

Buyer: https://backpack.tf/profiles/76561198316571500#!/compare/1550275200/1550361600

https://backpack.tf/item/7411377706

X = 10

Sale 2:

Sold for 10 keys

Seller: https://backpack.tf/profiles/76561198381463568#!/compare/1550448000/1550620800

Buyer: https://backpack.tf/profiles/76561198183877181#!/compare/1550534400/1550620800

https://backpack.tf/item/7411377706

X = 10

Sale 3:

Sold with 17 ref (~0.5) for 10 keys

Seller: https://backpack.tf/profiles/76561198264117106#!/compare/1550880000/1550966400

Buyer: https://backpack.tf/profiles/76561198264117106#!/compare/1550880000/1550966400

https://backpack.tf/item/7411377706

X = 9.5

Sale 4:

Sold to a bot for 8 keys

Seller: https://backpack.tf/profiles/76561198192293862#!/compare/1549324800/1549411200

Buyer: https://backpack.tf/profiles/76561198315588518#!/compare/1549324800/1549411200

https://backpack.tf/item/7468508061

X = 8

Sale 5:

Sold to a bot for 8 keys + 6 ref

Seller: https://backpack.tf/profiles/76561198224608640#!/compare/1551657600/1552694400

Buyer: https://backpack.tf/profiles/76561198005032783#!/compare/1551571200/1551657600

https://backpack.tf/item/7468508061

X = 8

Sale 6:

Sold for 8 keys

Seller: https://backpack.tf/profiles/76561198070151387#!/compare/1550275200/1552089600

Buyer: https://backpack.tf/profiles/76561198849487866#!/compare/1550275200/1550361600

https://backpack.tf/item/7411377706

X = 8

Marketplace Sales:

https://marketplace.tf/items/31034;5;u7

https://manic.tf/keyprice/?at=2019-02-06 - $18 / $1.81 = 9.94 keys

https://manic.tf/keyprice/?at=2019-03-01 - $18 / $1.78 = 10.11 keys

https://manic.tf/keyprice/?at=2019-03-02 - $29.88 / $1.79 = 16.69 keys

https://manic.tf/keyprice/?at=2019-03-08 - $25 / $1.8 = 13.89 keys

X = 17

X = 14

X = 10 (2x)

Other Sales:

https://backpack.tf/item/7508021391 (#1)

https://backpack.tf/item/7468508061 (#2 & #3)

https://backpack.tf/item/7424794637 (#4)

https://backpack.tf/item/7411377706 (#5 & #6)

#1

Untraceable

https://backpack.tf/profiles/76561198099780165#!/compare/1548979200/1549238400

https://backpack.tf/profiles/76561198005032783#!/compare/1548892800/1548979200

#2

Untraceable

https://backpack.tf/profiles/76561198315588518#!/compare/1549670400/1549843200

https://backpack.tf/profiles/76561198117433241#!/compare/1549756800/1549843200

https://i.imgur.com/ApmRMeI.png - Labelled as 10 keys

#3

Untraceable

https://backpack.tf/profiles/76561198108905664#!/compare/1551484800/1551571200

https://backpack.tf/profiles/76561198224608640#!/compare/1551571200/1551657600

#4

Bulk for Strange Scorching Brass Bucket

https://backpack.tf/profiles/76561198035463839#!/compare/1546214400/1546300800

https://backpack.tf/profiles/76561197994697258#!/compare/1546214400/1546300800

#5

Bulk-ish for Magnetic Hat Protector Phononaut

https://backpack.tf/profiles/76561198183877181#!/compare/1550880000/1550966400

https://backpack.tf/profiles/76561198264117106#!/compare/1550880000/1550966400

Using on the Phononaut.

#6

Sold for Miami Nights Respectless Robo-Glove

https://backpack.tf/profiles/76561198316571500#!/compare/1550361600/1550448000

https://backpack.tf/profiles/76561198381463568#!/compare/1550361600/1550448000

Can be used on the Glove.

Sellers:

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

https://backpack.tf/item/7508021391 - 11 keys

https://backpack.tf/item/7411377706 - 12 keys

Sales at:

8 (3x)

9.5

10 (4x)

14

17

Sellers at 11 and 12, excluding 14 and 17.

Sales at 8 are too common to be excluded. Keeping 8.

Going with 8-10.