Using last month.

Sales 1-3:

Sold for $20, $19.78 and $8 on marketplace.tf

https://marketplace.tf/items/477;5;u3004

20/1.97 = ~10.2

19.78/1.97 = ~10

8/1.97 = ~4.06

X = 10 (2x)

X = 4

Sale 4:

Sold for 9 keys

Seller: https://backpack.tf/profiles/76561198334598690#!/compare/1526860800/1526947200

Buyer: https://backpack.tf/profiles/76561198113057798#!/compare/1526860800/1527033600

Bot.tf confirms: https://i.imgur.com/iwa0otr.png

X = 9

Sale 5:

Sold for 7 keys

Seller: https://backpack.tf/profiles/76561198059021831#!/compare/1527206400/1527292800

Buyer: https://backpack.tf/profiles/76561198112652178#!/compare/1526947200/1527292800

X = 7

Sale 6:

Sold for 7 keys

Seller: https://backpack.tf/profiles/76561198011321852#!/compare/1527811200/1527897600

Buyer: https://backpack.tf/profiles/76561198033966344#!/compare/1526688000/1527897600

X = 7

Sale 7:

Sold for ~6 keys in items

Seller: https://backpack.tf/profiles/76561198089253101#!/compare/1526688000/1526774400

Buyer: https://backpack.tf/profiles/76561198245415708#!/compare/1526688000/1526774400

Probably not the best sale to use, but it should fit in the range anyways.

X = 6

Sale 8:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1526947200/1527033600

https://backpack.tf/item/6843484012 - buyer is untraceable

Bot.tf confirms: https://i.imgur.com/iwa0otr.png

X = 6

Sale 9:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1525910400/1525996800

Buyer: https://backpack.tf/profiles/76561198121061641#!/compare/1525996800/1526169600

Bot.tf confirms: https://i.imgur.com/iwa0otr.png

X = 6

Sale 10:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1527984000/1528070400

Buyer: https://backpack.tf/profiles/76561198272032798#!/compare/1527984000/1528070400

Bot.tf confirms: https://i.imgur.com/2bx1WmV.png (different screenshot because this sale occurred while I was making this suggestion)

X = 6

Sale 11:

Sold for 6 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1527811200/1527897600

Buyer: https://backpack.tf/profiles/76561198026736504#!/compare/1527897600/1527984000

Bot.tf confirms: https://i.imgur.com/iwa0otr.png

X = 6

Sale 12:

Sold for 5 keys + 10 ref

Seller: https://backpack.tf/profiles/76561198048851745#!/compare/1526083200/1526169600

Buyer: https://backpack.tf/profiles/76561198091002525#!/compare/1526083200/1526169600

X = 5.5

Sale 13:

Sold to a bot for 5 keys

Seller: https://backpack.tf/profiles/76561198141152637#!/compare/1526169600/1526860800

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1526774400/1526860800

Bot.tf confirms: https://i.imgur.com/iwa0otr.png

X = 5

Sale 14:

Sold to a bot for 5 keys

Seller: https://backpack.tf/profiles/76561198082401774#!/compare/1525392000/1525478400

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1525392000/1525478400

Bot.tf confirms: https://i.imgur.com/iwa0otr.png

X = 5

Sale 15:

Sold to a bot for 5 keys

Seller: https://backpack.tf/profiles/76561198428625600#!/compare/1527379200/1527552000

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1527465600/1527552000

Bot.tf confirms: https://i.imgur.com/2bx1WmV.png

X = 5

Sale 16:

Sold to a bot for 5 keys

Seller: https://backpack.tf/profiles/76561198062365679#!/compare/1527984000/1528070400

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1527897600/1527984000

Bot.tf confirms: https://i.imgur.com/iwa0otr.png

X = 5

Sale 17:

Sold to a bot for 4 keys + 2 ref

Seller: https://backpack.tf/profiles/76561198065994454#!/compare/1526428800/1526515200

Buyer: https://backpack.tf/profiles/76561198334598690#!/compare/1526428800/1526515200

X = 4

Sale 18:

Sold for another load of items

Seller: https://backpack.tf/profiles/76561198245415708#!/compare/1526860800/1526947200

Buyer: https://backpack.tf/profiles/76561198141152637#!/compare/1526169600/1526860800

Not gonna bother calculating this one.

Sale 19:

Bulk for Steaming Pug

Seller: https://backpack.tf/profiles/76561198124746619#!/compare/1526601600/1526688000

Buyer: https://backpack.tf/profiles/76561198059021831#!/compare/1526601600/1526688000

Sale 20:

Bulk for DBD Dark Falkirk

Seller: https://backpack.tf/profiles/76561198033885095#!/compare/1525737600/1526342400

Buyer: https://backpack.tf/profiles/76561198009927672#!/compare/1525651200/1525737600

Sale 21:

Sold for Steaming Gym Rat

http://www.tf2outpost.com/trade/29672601 - B/O of 9

Seller: https://backpack.tf/profiles/76561198356853241#!/compare/1527897600/1527984000

Buyer: https://backpack.tf/profiles/76561198062365679#!/compare/1527897600/1527984000

Plenty of pure sales here, would rather stick with them. This’ll end up being around 8-9 keys, though.

Sellers:

10 keys:

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

https://backpack.tf/item/6785919159

https://backpack.tf/item/2655718051

22 keys:

https://i.imgur.com/G8G9Vs3.png

https://backpack.tf/item/4392322275

And 2 sellers on the SCM at ~6 and ~8 keys:

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

Sales at:

4 (2x)

5 (4x)

5.5

6 (5x)

7 (2x)

9

10 (2x)

And another sale at ~8-9.

4 looks pretty low, excluding 4.

Sales at 9 and higher aren’t very common, and the majority of them aren’t pure keys. Excluding 9+.

Going with 5-7.