Sale 1:

Sold for 20 keys (ID’s match). Metal wasn’t involved, ID’s are too far apart.

Seller: https://backpack.tf/profiles/76561198312583107#!/compare/1532304000/1532390400

Buyer: https://backpack.tf/profiles/76561198058185986#!/compare/1532044800/1532476800

Bot.tf confirms: https://i.imgur.com/Ms4xER1.png

X = 20

Sale 2:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198141054773#!/compare/1532044800/1532131200

Buyer: https://backpack.tf/profiles/76561198254039408#!/compare/1532044800/1532131200

X = 18

Sale 3:

Sold to a bot for 16 keys + 1.11 ref

Seller: https://backpack.tf/profiles/76561198072561075#!/compare/1532044800/1532131200

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1532131200/1532649600

Bot.tf confirms: https://i.imgur.com/Ms4xER1.png

X = 16

Sale 4:

Sold to a bot for 16 keys + 1.11 ref?

Buyer: https://backpack.tf/profiles/76561198312583107#!/compare/1532044800/1532131200

https://backpack.tf/item/6855604872 - Seller’s compare link is private, assuming the buyer is visible in the histories here.

Bot.tf confirms, but it is unreliable. https://i.imgur.com/Ms4xER1.png

X = 16?

Sales 5 & 6:

Sold for $57.58 and $55.55 on marketplace.tf

https://marketplace.tf/items/1162;5;u3005

Both sales are going to be significantly higher than current sellers/sales. Excluding them.

Sale 7:

Bulk for Strange Burning Field Practice

Seller: https://backpack.tf/profiles/76561198049265461#!/compare/1532131200/1532217600

Buyer: https://backpack.tf/profiles/76561198396499936#!/compare/1532044800/1532131200

Sellers:

20 keys:

https://i.imgur.com/6jnhYZX.png

https://backpack.tf/item/4449514224

22 keys:

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

https://backpack.tf/item/4461235317

27 keys:

https://i.imgur.com/EiGvq8V.png

https://backpack.tf/item/4822664179

30 keys:

https://i.imgur.com/Rr30vnQ.png

https://backpack.tf/item/6346312418

Sales at:

16

18

20

And an untraceable sale at 16.

16 went to a quickbuyer/bot, and is not a common trading point. Excluding 16.

Going with 18-20.