Sales 1, 2, 3, 4, 5 & 6:

Sold for $39.99, $37, $25.09, $25, $24.99 and $24.96 on Marketplace.tf

https://marketplace.tf/items/30621;5;u3010

39.99/1.97 = ~20.3

37/1.96 = ~18.9

25.09/1.97 = ~12.7

25/1.95 = ~12.8

24.99/1.97 = ~12.7

24.96/1.97 = ~12.7

X = 20

X = 19

X = 13 (4x)

Sale 7:

Sold for 7 keys + Crusader’s Getup (2)

Seller: https://backpack.tf/profiles/76561198097271466#!/compare/1524787200/1524873600

Buyer: https://backpack.tf/profiles/76561198079848769#!/compare/1524787200/1524873600

X = 9

Sale 8:

Quicksold for 7 keys + 26 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1524096000/1524182400

Buyer: https://backpack.tf/profiles/76561198315531769#!/compare/1524009600/1524182400

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

X = 8

Sale 9:

Quicksold for 7 keys + 26 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1523836800/1523923200

https://backpack.tf/item/4357633809 - This is not the correct buyer, must’ve gone to someone who didn’t have their backpack scanned during the time they owned the taunt.

Untraceable, but Bot.tf confirms: https://i.imgur.com/GayuBlT.png

X = 8

Sale 10:

Quicksold for 7 keys + 26 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1524182400/1524268800

Buyer: https://backpack.tf/profiles/76561198193601761#!/compare/1524182400/1524268800

Untraceable, but Bot.tf confirms: https://i.imgur.com/GayuBlT.png

https://backpack.tf/item/5104746034

X = 8

Sale 11:

Quicksold for 8 keys + 4 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1523577600/1523664000

Buyer: https://backpack.tf/profiles/76561198071014143#!/compare/1523404800/1523836800

Untraceable, but bot.tf confirms: https://i.imgur.com/GayuBlT.png

X = 8

Sale 12:

Bulk for Haunted Ghosts Tundra Cap

Seller: https://backpack.tf/profiles/76561198189204270#!/compare/1524096000/1524182400

Buyer: https://backpack.tf/profiles/76561198046921199#!/compare/1524096000/1524182400

None of the strange ones have sales.

Sellers:

15 keys:

https://i.imgur.com/riYXFK7.png

https://backpack.tf/item/4734972893 - Strange

https://backpack.tf/item/4598606407

19 keys:

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

https://backpack.tf/item/4441800251 - Strange

20 keys:

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

https://backpack.tf/item/4385517503 - Strange

207.5 keys:

http://www.tf2outpost.com/trade/28688408 - Strange

Offers:

http://www.tf2outpost.com/trade/29639762

http://www.tf2outpost.com/trade/29436851

And a seller for ~10 keys worth ($20) on Marketplace.tf:

https://marketplace.tf/items/30621;5;u3010

https://backpack.tf/item/5104746034

Sales at:

8 (4x)

9

13 (4x)

19

20

This one’s tricky.

19 and 20 are outliers, excluding.

https://i.imgur.com/zIDC9kD.png - Highest buyer at 9 keys. Knowing them, they’re most likely looking for something overpriced for reasons and will most likely remove their buy order when this suggestion get submitted. Second highest buyer is ~7. For this reason, I will not exclude 9.

I will exclude 8, however, as every sale at 8 appears to have sold in a day.

Going with a hideous range of 9-13.