Using last 2 months (last 1 month wasn’t cutting it here)

Sale 1:

Sold for 4 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198011168187#!/compare/1558224000/1558310400

Buyer: https://backpack.tf/profiles/76561198340634356#!/compare/1558224000/1558310400

https://backpack.tf/item/4962996061

https://i.imgur.com/S7gGdBV.png - bot.tf confirms

X = 4.5

Sale 2:

Sold for 4 keys + ~0.5 keys in metal

Seller: https://backpack.tf/profiles/76561198230105584#!/compare/1554508800/1554595200

Buyer: https://backpack.tf/profiles/76561198379270361#!/compare/1554595200/1554681600

X = 4.5

Sale 3:

Sold for 4 keys + 12 ref

Seller: https://backpack.tf/profiles/76561198321496837#!/compare/1554595200/1554854400

Buyer: https://backpack.tf/profiles/76561198230105584#!/compare/1554508800/1554595200

https://backpack.tf/item/6983603598

X = 4.5

Sale 4:

Sold for 4 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198829155436#!/compare/1558396800/1558483200

Buyer: https://backpack.tf/profiles/76561198141455733#!/compare/1558224000/1558396800

https://backpack.tf/item/5382655424

X = 4

Other Sales:

https://backpack.tf/item/5383277655 (#1)

https://backpack.tf/item/6983603598 (#2-4)

https://backpack.tf/item/5332229133 - tradeit

https://backpack.tf/item/6501988534 - marketplace

https://backpack.tf/item/6417560594 - marketplace and stuff

https://backpack.tf/item/7420171429 - scrap, and unscanned backpack to a bot

https://i.imgur.com/S7gGdBV.png - the bot purchase above labelled as 4 keys + 20 ref

#1

SCM

https://backpack.tf/profiles/76561198197898870#!/compare/1553990400/1554422400

https://backpack.tf/profiles/76561198326837245#!/compare/1553904000/1555286400

#2

Untraceable

https://backpack.tf/profiles/76561198379270361#!/compare/1554595200/1554681600

https://backpack.tf/profiles/76561198924108038#!/compare/1554076800/1554681600

#3

Untraceable, only the Showstopper Burstchester matches

https://backpack.tf/profiles/76561198924108038#!/compare/1554076800/1554681600

https://backpack.tf/profiles/76561198809654499#!/compare/1554508800/1554681600

#4

Untraceable, most likely sold for 4 keys + 10 ref

https://backpack.tf/profiles/76561198809654499#!/compare/1554508800/1554681600

https://backpack.tf/profiles/76561198335791307#!/compare/1554595200/1554681600

Not presented on bot.tf.

Sellers:

https://i.imgur.com/IY6yuFl.png

https://backpack.tf/item/5382655424 - ~4.65 keys

https://backpack.tf/item/7420171429 - ~4.85 keys

https://backpack.tf/item/6983603598 - ~4.85 keys

https://backpack.tf/item/4990359398 - 6 keys

https://backpack.tf/item/5277050790 - 12 keys

Sales at:

4

4.5 (3x)

Buyers at 4+, excluding 4.

Going with 4.5 flat.