Sales 1, 2 & 3:

Sold for $8, $12 and $13.89 on Marketplace.tf

https://marketplace.tf/items/477;5;u3009

13.89/1.99 = ~6.98

12/1.99 = ~6.03

8/1.99 = ~4.02

X = 7

X = 6

X = 4

Sale 4:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198344933095#!/compare/1523318400/1523404800

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

https://backpack.tf/item/2449733326 - Item history shows that it’s in the Freighter bot, so it’s likely that someone bought it then dumped it there before their backpack was scanned.

X = 6

Sale 5:

Sold for 5 keys + ~18 ref in metal/items

Seller: https://backpack.tf/profiles/76561198048851745#!/compare/1521936000/1522022400

Buyer: https://backpack.tf/profiles/76561198198286613#!/compare/1522022400/1522108800

X = 5.5

Sellers:

~6.35 keys:

https://i.imgur.com/4We4vqf.png ~25 days

https://backpack.tf/item/6571592662

10 keys:

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

https://backpack.tf/item/2214546444

~10.7 keys:

https://i.imgur.com/2El7Erk.png

https://backpack.tf/item/2639666175

Sales at:

4

5.5

6 (2x)

7

Quickbuyers at ~4.3 keys, excluding 4.

Seller at ~6.35 keys is 25 days old, excluding 7.

Going with 5.5-6.