Sale 1:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198344933095#!/compare/1524614400/1524700800

https://backpack.tf/item/2946030951 - Couldn’t trace the buyer, it wasn’t the next person in the history because they got it at a later date.

Untraceable, but bot.tf confirms: https://i.imgur.com/NqASYYY.png

X = 6

Sale 2:

Sold for 6 keys (Buyer’s compare link)

Seller: https://backpack.tf/profiles/76561198044335614#!/compare/1523664000/1523750400

Buyer: https://backpack.tf/profiles/76561198067663328#!/compare/1523664000/1523750400

X = 6

Sale 3:

Sold for 5 keys

Seller: https://backpack.tf/profiles/76561198129205357#!/compare/1523750400/1523836800

Buyer: https://backpack.tf/profiles/76561198182051303#!/compare/1514764800/1523836800

X = 5

Sale 4:

Sold for 4 keys + 16 ref

Seller: https://backpack.tf/profiles/76561198162975881#!/compare/1524528000/1524614400

Buyer: https://backpack.tf/profiles/76561198352286528#!/compare/1524528000/1524614400

X = 4.5

Sale 5:

Sold for Kill-a-Watt Wet Works

Seller: https://backpack.tf/profiles/76561198067663328#!/compare/1523664000/1523750400

Buyer: https://backpack.tf/profiles/76561198334260642#!/compare/1523664000/1523750400

Large outlier, excluding.

Sellers:

~6.6 keys:

https://i.imgur.com/iQhKG0M.png

https://backpack.tf/item/2974752288

~6.9 keys:

https://i.imgur.com/328EVaq.png

https://backpack.tf/item/3714139084

~7 keys:

https://i.imgur.com/j8b4Ec3.png

https://backpack.tf/item/3275106007

https://backpack.tf/item/3194054017

Sales at:

4.5

5

6 (2x)

Going with 4.5-6.