Using sales that were less than a month old when I started making this suggestion (29/9)

Sale 1:

Sold for $14.50 on marketplace.tf

https://marketplace.tf/items/1112;5;u3006

http://manic.tf/keyprice/?at=2018-09-06 - $14.5 / $1.88 = 7.71 keys

Can’t find item history.

X = 7.5

Sale 2:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198271114604#!/compare/1536624000/1537056000

Buyer: https://backpack.tf/profiles/76561198210666103#!/compare/1536105600/1537574400

https://backpack.tf/item/6374097722

X = 6

Sale 3:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198363395191#!/compare/1536019200/1536105600

Buyer: https://backpack.tf/profiles/76561198127941447#!/compare/1535932800/1536105600

https://backpack.tf/item/6286967401

X = 6

Sale 4:

Sold for 5 keys + 20 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1536710400/1536796800

Buyer: https://backpack.tf/profiles/76561198046941961#!/compare/1536192000/1536796800

https://backpack.tf/item/2762894060

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

X = 5.5

Other Sales:

https://backpack.tf/item/6999856475 (#1)

https://backpack.tf/item/4140978340 (#2)

https://backpack.tf/item/3317392642 - tf2mart

https://backpack.tf/item/5595979464 - tf2mart

https://backpack.tf/item/5270021699 - tf2mart

https://backpack.tf/item/2853381887 - tradeit

https://backpack.tf/item/3417634257 - marketplace

#1

Untraceable

https://backpack.tf/profiles/76561198091786633#!/compare/1535500800/1536624000

https://backpack.tf/profiles/76561198254039408#!/compare/1535673600/1536710400

#2

Untraceable

https://backpack.tf/profiles/76561198054887218#!/compare/1537660800/1537747200

https://backpack.tf/profiles/76561198279848751#!/compare/1537660800/1537833600

Can almost guarantee it sold for 6 keys

Bot.tf shows a bot purchase at 4 keys:

https://i.imgur.com/5Wrf7eT.png

https://backpack.tf/profiles/76561198295122993#!/compare/1538776800/1538863200

but we can’t even see the item history. Even if it were usable, I’d exclude it due to it not being a common trading point, combined with the 2 buyers at 4+ keys

Sellers:

https://i.imgur.com/6pjxHI5.png

https://backpack.tf/item/4140978340 - 7 keys

https://backpack.tf/item/3321535315 - 8 keys

https://backpack.tf/item/4369484348 - 14 keys

https://backpack.tf/item/5428330274 - 15 keys

Sales at:

5.5

6 (2x)

7.5

7.5 is too high given the unsold at 7 keys. Excluding 7.5.

Going with 5.5-6.

Sold for $12.99, $13, & $8.40 on marketplace

https://marketplace.tf/items/1112;5;u3006

https://manic.tf/keyprice/?at=2018-10-13 - $12.99 / $1.78 = 7.30 keys

https://manic.tf/keyprice/?at=2018-10-15 - $13 / $1.77 = 7.34 keys

https://manic.tf/keyprice/?at=2018-10-16 - $8.4 / $1.77 = 4.75 keys

X = 7.5 (2x)

X = 5

The sales at 7.5 look like outliers especially given the sellers at 7 keys, and the sale at 5 keys would've gone to a marketplace buy order, so i'll exclude these sales.

$6 on marketplace, way too low.

https://marketplace.tf/items/1112;5;u3006