Using last month.

Sales 1-4:

Sold for $20.98, $20.80 (2x), & $20.69

https://marketplace.tf/items/1106;5;u3003

https://manic.tf/keyprice/?at=2018-09-23 - $20.98 / $1.84 = 11.40 keys

https://manic.tf/keyprice/?at=2018-09-29 - $20.8 / $1.84 = 11.30 keys

https://manic.tf/keyprice/?at=2018-09-30 - $20.8 / $1.84 = 11.30 keys

https://manic.tf/keyprice/?at=2018-09-30 - $20.69 / $1.84 = 11.24 keys

X = 11 (4x)

Sale 5:

Sold for 11 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1538006400/1538092800

Buyer: https://backpack.tf/profiles/76561198279527155#!/compare/1537920000/1538352000

https://backpack.tf/item/5935964111

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

X = 11

Sale 6:

Sold for 9 keys + ~0.5 keys in ref

Seller: https://backpack.tf/profiles/76561198184669555#!/compare/1538352000/1538784000

Buyer: https://backpack.tf/profiles/76561198044335614#!/compare/1538697600/1538784000

https://backpack.tf/item/4919778306

The seller spent some ref on a key after the sale, so some of the histories of the ref on the buyer’s end went to the previous key’s owner.

X = 9.5

Sale 7:

Sold for 9 keys + ~0.5 keys in ref

Seller: https://backpack.tf/profiles/76561198271521289#!/compare/1539475200/1539561600

Buyer: https://backpack.tf/profiles/76561198335791307#!/compare/1539475200/1539561600

https://backpack.tf/item/4204442255

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

X = 9.5

Sale 8:

Sold for 9 keys + ~0.5 keys in ref

Seller: https://backpack.tf/profiles/76561198112281935#!/compare/1537574400/1537660800

Buyer: https://backpack.tf/profiles/76561198335791307#!/compare/1537574400/1537660800

https://backpack.tf/item/2878202808

X = 9.5

Other Sales:

https://backpack.tf/item/5935964111 (#1 & #2)

https://backpack.tf/item/3692758169 (#3)

https://backpack.tf/item/3067645243 (#4)

https://backpack.tf/item/2878202808 (#5 & #6)

https://backpack.tf/item/2710496141 (#7)

https://backpack.tf/item/3459652020 - tf2mart

https://backpack.tf/item/6799189523 - marketplace

https://backpack.tf/item/4367316226 - tf2mart

#1

Untraceable

https://backpack.tf/profiles/76561198388933135#!/compare/1537488000/1537574400

https://backpack.tf/profiles/76561198305676157#!/compare/1537401600/1537488000

https://i.imgur.com/DTmzcvV.png - labelled as 9 keys + 19 ref

#2

Probably gambled

https://backpack.tf/profiles/76561198279527155#!/compare/1538352000/1538697600

https://backpack.tf/profiles/76561198133540930#!/compare/1538265600/1538352000

#3

Untraceable

https://backpack.tf/profiles/76561198448830963#!/compare/1537660800/1537747200

https://backpack.tf/profiles/76561198170967426#!/compare/1537660800/1537747200

#4

SCM

https://backpack.tf/profiles/76561198257090946#!/compare/1537056000/1539561600

https://backpack.tf/profiles/76561198064490192#!/compare/1538438400/1538524800

#5

Bulk for a war paint

https://backpack.tf/profiles/76561198399031554#!/compare/1537488000/1537574400

https://backpack.tf/profiles/76561198112281935#!/compare/1537574400/1537660800

#6

Untraceable

https://backpack.tf/profiles/76561198335791307#!/compare/1539302400/1539388800

https://backpack.tf/profiles/76561198045447325#!/compare/1539302400/1539388800

https://i.imgur.com/DTmzcvV.png - labelled as 11 keys

Only 9 keys match. Fine to exclude as we have many other sales to use here.

#7

Untraceable

https://backpack.tf/profiles/76561198839307425#!/compare/1538092800/1538179200

https://backpack.tf/profiles/76561198176948939#!/compare/1538092800/1538179200

https://i.imgur.com/DTmzcvV.png - labelled as 11 keys + 5 ref

Sellers:

https://i.imgur.com/7dgXQaQ.png

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

https://backpack.tf/item/5935964111 - 10 keys

https://backpack.tf/item/4204442255 - 11 keys

https://backpack.tf/item/4351600757 - 11 keys

https://backpack.tf/item/6902909296 - ~11.25 keys

https://backpack.tf/item/6779193085 - ~11.25 keys

https://backpack.tf/item/3853118691 - ~11.65 keys

https://backpack.tf/item/6568327542 - 18 keys

Sales at:

11 (5x)

9.5 (3x)

9.5 is a common trading point, shouldn’t exclude due to buyers.

Going with 9.5-11.