Sale 1:

Sold for 15 keys + more than half a key in items

http://www.tf2outpost.com/trade/29711537 - B/O of 17

Seller: https://backpack.tf/profiles/76561198133111079#!/compare/1531785600/1531872000

Buyer: https://backpack.tf/profiles/76561198071474738#!/compare/1531785600/1531872000

https://backpack.tf/item/6833515404

X = 16

Sale 2:

Sold for 14 keys

Seller: https://backpack.tf/profiles/76561198160856661#!/compare/1531440000/1531526400

Buyer: https://backpack.tf/profiles/76561198133111079#!/compare/1531440000/1531526400

https://backpack.tf/item/6833515404

X = 14

Sale 3:

Sold for 12 keys + ~1 key in items

Seller: https://backpack.tf/profiles/76561198050114720#!/compare/1531958400/1532044800

Buyer: https://backpack.tf/profiles/76561198249179302#!/compare/1531785600/1532044800

https://backpack.tf/item/6833515404

X = 13

Sale 4:

Sold for 13 keys

Seller: https://backpack.tf/profiles/76561198249179302#!/compare/1532563200/1532908800

Buyer: https://backpack.tf/profiles/76561198239282272#!/compare/1532822400/1532908800

https://backpack.tf/item/6833515404

X = 13

Sale 5:

Sold to scrap for ~12 keys

Seller: https://backpack.tf/profiles/76561198047941585#!/compare/1533513600/1533600000

Buyer: https://backpack.tf/profiles/76561198135388328#!/compare/1533513600/1533600000

https://backpack.tf/item/6943053901

X = 12

Other Sales:

https://backpack.tf/item/6943053901 (#1 & #2)

https://backpack.tf/item/6833515404 (#3-6)

#1

Bulk

https://backpack.tf/profiles/76561198158748076#!/compare/1532822400/1532995200

https://backpack.tf/profiles/76561198047941585#!/compare/1532908800/1532995200

#2

Untraceable, bought from scrap.tf

https://backpack.tf/profiles/76561198135388328#!/compare/1533513600/1533600000

https://backpack.tf/profiles/76561198448207173#!/compare/1533340800/1533686400

#3

Bulk for Stare From Beyond Combustible Kabuto

https://backpack.tf/profiles/76561198071474738#!/compare/1531785600/1531872000

https://backpack.tf/profiles/76561198382076026#!/compare/1531526400/1531872000

#4

Untraceable, sold to scrap.tf

https://backpack.tf/profiles/76561198382076026#!/compare/1531872000/1531958400

https://backpack.tf/profiles/76561198135388328#!/compare/1531785600/1531872000

#5

Untraceable, bought from scrap.tf

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

https://backpack.tf/profiles/76561198058266974#!/compare/1531872000/1531958400

#6

Bulk for Kill-a-Watt KE

https://backpack.tf/profiles/76561198058266974#!/compare/1531872000/1531958400

https://backpack.tf/profiles/76561198050114720#!/compare/1531872000/1531958400

Sellers:

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

https://backpack.tf/item/6943053901

Sales at:

12

13 (2x)

14

16

https://i.imgur.com/ZdDGHBn.png - Buyer at 12, excluding 12.

Not sure if excluding 12 is a good idea, same for keeping 16.

Going with 13-16.