Sale 1:

Sold for 11 keys

Seller: https://backpack.tf/profiles/76561198054758757#!/compare/1536969600/1537056000

Buyer: https://backpack.tf/profiles/76561198414515070#!/compare/1536969600/1537056000

https://backpack.tf/item/4400607019

X = 11

Sale 2:

Sold for 10 keys + Strange Natascha

Seller: https://backpack.tf/profiles/76561198047819527#!/compare/1531180800/1531267200

Buyer: https://backpack.tf/profiles/76561198083485457#!/compare/1528416000/1531267200

https://backpack.tf/item/2157011575

X = 10

Sale 3:

Sold for 9 keys

Seller: https://backpack.tf/profiles/76561198155228080#!/compare/1530748800/1531094400

Buyer: https://backpack.tf/profiles/76561198054758757#!/compare/1530748800/1530835200

https://backpack.tf/item/2157011575

X = 9

Sale 4:

Sold for $15 on marketplace.tf

https://marketplace.tf/items/437;5;u57

https://backpack.tf/item/4400607019

Gonna be way too low, excluding.

Other Sales:

https://backpack.tf/item/6756411141 (#1 & #2)

https://backpack.tf/item/4400607019 (#3 & #4)

https://backpack.tf/item/2157011575 (#5-9)

https://backpack.tf/item/1945005345 (#10)

#1

Untraceable, bought from scrap

https://backpack.tf/profiles/76561198135388328#!/compare/1533427200/1533513600

https://backpack.tf/profiles/76561198182019834#!/compare/1533168000/1533686400

#2

Untraceable, sold to scrap

https://backpack.tf/profiles/76561198182019834#!/compare/1533686400/1534550400

https://backpack.tf/profiles/76561198135388328#!/compare/1534377600/1534464000

#3

Sold to and from scrap

https://backpack.tf/profiles/76561198135388328#!/compare/1531872000/1531958400

https://backpack.tf/profiles/76561198088764747#!/compare/1531872000/1531958400

#4

Untraceable, bought from scrap

https://backpack.tf/profiles/76561198135388328#!/compare/1532131200/1532217600

https://backpack.tf/profiles/76561198074153368#!/compare/1532131200/1532217600

#5

Untraceable

https://backpack.tf/profiles/76561198363135118#!/compare/1530403200/1530489600

https://backpack.tf/profiles/76561198123631904#!/compare/1530403200/1530489600

#6

Untraceable

https://backpack.tf/profiles/76561198054758757#!/compare/1531008000/1531094400

https://backpack.tf/profiles/76561198224348988#!/compare/1531008000/1531180800

#7

Untraceable

https://backpack.tf/profiles/76561198083485457#!/compare/1531440000/1531526400

https://backpack.tf/profiles/76561198337734785#!/compare/1531353600/1531440000

#8

Bulk for pure

https://backpack.tf/profiles/76561198337734785#!/compare/1533686400/1533772800

https://backpack.tf/profiles/76561198218497692#!/compare/1533686400/1533772800

#9

Bulk for Burning Runner’s Warm-up

https://backpack.tf/profiles/76561198218497692#!/compare/1533945600/1534032000

https://backpack.tf/profiles/76561198112510439#!/compare/1533945600/1534032000

#10

Untraceable

https://backpack.tf/profiles/76561198142972676#!/compare/1533254400/1533427200

https://backpack.tf/profiles/76561198132324798#!/compare/1531958400/1533427200

Sellers:

https://i.imgur.com/0pO3Cw4.png

https://backpack.tf/item/5391477946 - 11 keys

https://backpack.tf/item/2885568451 - 12 keys

https://backpack.tf/item/4400607019 - ~12.13 keys

https://backpack.tf/item/2157011575 - 14 keys

Sales at:

9

10

11

https://i.imgur.com/Bl0NGRQ.png - Buyer at 9, excluding 9.

Going with 10-11.