Sale 1:

Sold for 10 keys + 17 ref

Seller: https://backpack.tf/profiles/76561198146640595#!/compare/1515456000/1515542400

Buyer: https://backpack.tf/profiles/76561198163588493#!/compare/1515456000/1515542400

X = 11

Sale 2:

Sold with cheap fabricators for Fountain of Delight Bad Pipes (10.5) + cheap amount of ref

No outpost

Seller: https://backpack.tf/profiles/76561198163588493#!/compare/1519257600/1519344000

Buyer: https://backpack.tf/profiles/76561198346506937#!/compare/1519084800/1519344000

X = 11

Sale 3:

Quicksold for 10 keys

Seller: https://backpack.tf/profiles/76561198215842352#!/compare/1520812800/1520899200

Buyer: https://backpack.tf/profiles/76561198006295346#!/compare/1520812800/1520899200

X = 10

Sale 4:

Quicksold for 9 keys

Seller: https://backpack.tf/profiles/76561198212547641#!/compare/1518480000/1518652800

Buyer: https://backpack.tf/profiles/76561198142160712#!/compare/1518480000/1518652800

X = 9

Sale 5:

Sold for 9 keys

Seller: https://backpack.tf/profiles/76561198310144372#!/compare/1518739200/1518825600

Buyer: https://backpack.tf/profiles/76561198197255435#!/compare/1518739200/1518825600

X = 9

Sale 6:

Quicksold for 8 keys + 10 ref

Seller: https://backpack.tf/profiles/76561198272058312#!/compare/1520726400/1520812800

Buyer: https://backpack.tf/profiles/76561198215842352#!/compare/1520726400/1520812800

X = 8.5

Sale 7:

Quicksold for 8 keys + 12 ref

Seller: https://backpack.tf/profiles/76561198254146665#!/compare/1518480000/1518652800

Buyer: https://backpack.tf/profiles/76561198212547641#!/compare/1518480000/1518652800

X = 8.5

Sale 8:

Sold to a bot for 8 keys + 2 ref

Seller: https://backpack.tf/profiles/76561198142160712#!/compare/1518480000/1518652800

Buyer: https://backpack.tf/profiles/76561198310144372#!/compare/1518566400/1518652800

X = 8

Sale 9:

Sold for SGG Skullcracker + ~7 keys worth of pure/items

No outpost

Seller: https://backpack.tf/profiles/76561198125082062#!/compare/1520035200/1520726400

Buyer: https://backpack.tf/profiles/76561198807602991#!/compare/1520640000/1520726400

Way too high.

Sale 10:

Sold for Results Unusualifier

Seller: https://backpack.tf/profiles/76561198286453411#!/compare/1519948800/1520035200

Buyer: https://backpack.tf/profiles/76561198160003206#!/compare/1520035200/1520812800

Unusualifier is going for ~5 keys on the SCM, excluding this sale.

Sale 11:

Sold with ~1 key in items for Screaming Tiger Soviet Strongarm

Seller: https://backpack.tf/profiles/76561198160003206#!/compare/1520812800/1520899200

Buyer: https://backpack.tf/profiles/76561198302114051#!/compare/1520640000/1520812800

Should be used on the Strongarm

Sellers:

11 keys:

https://i.imgur.com/gQk9zCH.png

https://backpack.tf/item/6419110762

Sales at:

8

8.5 (2x)

9 (2x)

10

11 (2x)

Sales around 9 keys are far too common to be excluded. Will exclude sales under 9, however.

Going with 9-11.