Using last month.

Sales 1 & 2:

Sold for $15.99 and $15 on marketplace.tf

https://marketplace.tf/items/1112;5;u3004

15.99/1.98 = ~8.08

15/1.97 = ~7.61

X = 8

X = 7.5

Sale 3:

Sold for 7 keys

Seller: https://backpack.tf/profiles/76561198044335614#!/compare/1525046400/1525132800

Buyer: https://backpack.tf/profiles/76561198066678954#!/compare/1524700800/1525132800

X = 7

Sale 4:

Sold for ~5 keys worth of items that are, or used to be, considered a currency (Buyer’s end)

Seller: https://backpack.tf/profiles/76561198102063164#!/compare/1525737600/1525824000

Buyer: https://backpack.tf/profiles/76561198293690438#!/compare/1525392000/1525996800

X = 5

Sale 5:

Sold to a bot for 4 keys + 3 ref

Seller can’t be traced - https://backpack.tf/item/2730494500

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1527638400/1527724800

Bot.tf confirms: https://i.imgur.com/9eeJ5QB.png

X = 4

Sellers:

~5.5 keys:

https://i.imgur.com/c2CiZhL.png

https://backpack.tf/item/2730494500

6 keys:

https://i.imgur.com/zyx3e7K.png

https://backpack.tf/item/2747380497

7 keys:

https://i.imgur.com/9m1aVhs.png

https://backpack.tf/item/2874801530

11 keys:

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

https://backpack.tf/item/6495346961

Sales at:

4

5

7

7.5

8

Wanted to exclude anything higher than the sellers due to one of them being almost a month old, but these sales suck, and they occupy the majority of sales here. Excluding the marketplace sales, though (7.5 and 8).

4 seems kinda low, excluding 4.

Going with 5-7.