Using last month.

Sale 1:

Sold for Slumber Stove Pipe (21)

http://www.tf2outpost.com/trade/29635348 - B/O of ~12

Seller: https://backpack.tf/profiles/76561198063041674#!/compare/1524960000/1525046400

Buyer: https://backpack.tf/profiles/76561198104019775#!/compare/1523836800/1525046400

X = 12 (Capped by B/O)

Sale 2:

Sold for 7 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1524873600/1524960000

Buyer: https://backpack.tf/profiles/76561198063041674#!/compare/1524960000/1525046400 (backpack wasn’t scanned before trade)

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

X = 7

Sale 3:

Sold for 7 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1525996800/1526083200

Buyer: https://backpack.tf/profiles/76561198270931078#!/compare/1525996800/1526083200

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

X = 7

Sale 4:

Sold to a bot for 6 keys + 6 ref

Seller: https://backpack.tf/profiles/76561198158206236#!/compare/1523750400/1525996800

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1525996800/1526083200

X = 6

Sale 5:

Sold to a bot for 6 keys + 6 ref

Buyer: https://backpack.tf/profiles/76561198305676157#!/compare/1526688000/1526774400

https://backpack.tf/item/6360404644 - Seller doesn’t appear to be traceable

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

X = 6

Sale 6:

Bulk for Showstopper Schadenfreude

Seller: https://backpack.tf/profiles/76561198072945055#!/compare/1526688000/1526774400

Buyer: https://backpack.tf/profiles/76561198136987862#!/compare/1526688000/1526774400

Sellers:

~7 keys:

https://i.imgur.com/q9bB21S.png

https://backpack.tf/item/6360404644

https://backpack.tf/item/6261532570

https://backpack.tf/item/6392390129

https://backpack.tf/item/6258426386

https://backpack.tf/item/6357465973

8 keys:

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

https://backpack.tf/item/6256280364

~10.5 keys:

https://i.imgur.com/plHC8XL.png

https://backpack.tf/item/6274930002

34 keys:

https://i.imgur.com/2qrbYs0.png

https://backpack.tf/item/6436760501

Sales at:

6 (2x)

7 (2x)

12

12 is an outlier, excluding 12.

Going with 6-7.