Re-suggesting, using sales from the last suggestion onwards.

Sales 1-4:

Sold for $25.99, $23.49, $23.99, and $20.65 on marketplace.tf

https://marketplace.tf/items/1107;5;u3005

https://backpack.tf/item/6272097802 - No outpost

https://backpack.tf/item/2895117342 - No outpost

Couldn’t find the others.

http://manic.tf/keyprice/?at=2018-07-28 - 23.99/1.99 = ~12.06

http://manic.tf/keyprice/?at=2018-08-08 - $20.65 / $1.89 = 10.93 keys

http://manic.tf/keyprice/?at=2018-08-25 - $25.99 / $1.9 = 13.68 keys

http://manic.tf/keyprice/?at=2018-08-29 - $23.49 / $1.88 = 12.49 keys

X = 14

X = 12 (2x)

X = 11

Sale 5:

Sold for Grail Rock, Paper, Scissors (12.5)

http://www.tf2outpost.com/trade/29698620 - No visible B/O

Seller: https://backpack.tf/profiles/76561198124728984#!/compare/1534464000/1534550400

Buyer: https://backpack.tf/profiles/76561198110267417#!/compare/1534377600/1534550400

https://backpack.tf/item/4823906087

X = 13

Sale 6:

Sold to a bot for 8 keys + small amount of metal

https://backpack.tf/profiles/76561198054678875#!/compare/1535500800/1535587200

https://backpack.tf/profiles/76561198839307425#!/compare/1535500800/1535587200

https://gyazo.com/e78f889a9dbd00fc9755ff47c4aa5c5b

https://backpack.tf/item/4128527418

X = 8

Sale 7:

Sold to a bot for 8 keys + 5 ref

https://backpack.tf/profiles/76561198179524514#!/compare/1535587200/1535673600

https://backpack.tf/profiles/76561198839307425#!/compare/1535587200/1535673600

https://gyazo.com/e78f889a9dbd00fc9755ff47c4aa5c5b

https://backpack.tf/item/2895117342

X = 8

Sale 8:

Sold to a quickbuyer for 7 keys + 15 ref

https://backpack.tf/profiles/76561198092615798#!/compare/1535068800/1535241600

https://backpack.tf/profiles/76561198080179568#!/compare/1535155200/1535241600

https://backpack.tf/item/2895117342

X = 7.5

Sale 9:

Sold for 7 keys and 16 ref to a bot

Seller: https://backpack.tf/profiles/76561198135348194#!/compare/1529539200/1533168000

Buyer: https://backpack.tf/profiles/76561198839307425#!/compare/1532988000/1533074400

https://backpack.tf/item/6103242563

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

Keys don’t appear in the seller’s end, but all the ref does. I highly doubt bot.tf is incorrect here.

X = 7.5

Other Sales:

https://backpack.tf/item/3707243587 (#1 & #2)

https://backpack.tf/item/3206576263 (#3 & #4)

https://backpack.tf/item/2895117342 (#5)

#1

https://backpack.tf/profiles/76561198188835167#!/compare/1534032000/1534204800

https://backpack.tf/profiles/76561198839307425#!/compare/1534204800/1534291200

https://gyazo.com/e78f889a9dbd00fc9755ff47c4aa5c5b

Labelled as a 7 key and 25 ref purchase.

#2

Untraceable

https://backpack.tf/profiles/76561198839307425#!/compare/1535241600/1535328000

https://gyazo.com/e78f889a9dbd00fc9755ff47c4aa5c5b - Labelled as 14 keys

#3

Bulk for Cloudy Moon Cotton Head

Seller: https://backpack.tf/profiles/76561198144628116#!/compare/1533168000/1534636800

Buyer: https://backpack.tf/profiles/76561198411930230#!/compare/1534550400/1534636800

#4

Bulk for Burning Nunhood

Seller: https://backpack.tf/profiles/76561198411930230#!/compare/1534636800/1534723200

Buyer: https://backpack.tf/profiles/76561198296076323#!/compare/1534636800/1534723200

https://backpack.tf/item/3206576263

#5

Untraceable, sold to a bot

https://backpack.tf/profiles/76561198844378729#!/compare/1535155200/1535587200

https://backpack.tf/profiles/76561198839307425#!/compare/1535500800/1535587200

https://gyazo.com/e78f889a9dbd00fc9755ff47c4aa5c5b - labelled as 8 keys + 5 ref

Sellers:

https://gyazo.com/01c652382c652f8224ceed69c9195757

https://gyazo.com/0ff01cc9fc1e905f91625128c10858d4

https://backpack.tf/item/2895117342 - 19 keys

https://backpack.tf/item/4128527418 - 19 keys

https://backpack.tf/item/2896727109 - 20 keys

https://backpack.tf/item/2712151582 - 25 keys

https://backpack.tf/item/3376555378 - 27 keys

https://backpack.tf/item/2818017541 - 40 keys

https://backpack.tf/item/2818017541 - 45 keys

Sales at:

7.5 (2x)

8 (2x)

11

12 (2x)

13

14

7.5 and 8 went to quickbuyers, excluding them.

Going with 11-14.