Sale 1:

Sold with ~2 keys in genuine items for Clairvoyance Highway Star (16)

Seller: https://backpack.tf/profiles/76561198187093225#!/compare/1547769600/1547856000

Buyer: https://backpack.tf/profiles/76561198847091856#!/compare/1547769600/1547856000

https://backpack.tf/item/920931920

X = 14

Sale 2:

Sold for 12 keys

Seller: https://backpack.tf/profiles/76561198124091633#!/compare/1547769600/1547856000

Buyer: https://backpack.tf/profiles/76561198187093225#!/compare/1547769600/1547856000

https://backpack.tf/item/920931920

X = 12

Sale 3:

Quicksold for 12 keys

Seller: https://backpack.tf/profiles/76561198847091856#!/compare/1547856000/1547942400

Buyer: https://backpack.tf/profiles/76561198273690159#!/compare/1547510400/1547942400

https://backpack.tf/item/920931920

X = 12

Sale 4:

Quicksold for 11 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198267589362#!/compare/1547510400/1547596800

Buyer: https://backpack.tf/profiles/76561198124091633#!/compare/1547424000/1547596800

https://backpack.tf/item/920931920

X = 11

Other Sales:

https://backpack.tf/item/920931920 (#1)

https://backpack.tf/item/415966133 - marketplace

https://backpack.tf/item/345930796 - marketplace

#1

Untraceable

https://backpack.tf/profiles/76561198354399482#!/compare/1546560000/1546646400

https://backpack.tf/profiles/76561198002757046#!/compare/1546473600/1546560000

#2

Untraceable

https://backpack.tf/profiles/76561198002757046#!/compare/1546819200/1546905600

https://backpack.tf/profiles/76561197995822698#!/compare/1546819200/1546905600

Sellers:

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

https://backpack.tf/item/345930796 - 15 keys

Sales at:

11

12 (2x)

14

Sales below 14 are too common to be excluded, even if some did quicksell. Will exclude 11 due to buyers, and keep 12.

Going with 12-14.