Using sales from last suggestion and onward.

Sales 1-4:

Sold for $59.99, $46.66, $28 and $21.99 on marketplace.tf

https://marketplace.tf/items/30762;5;u3004

59.99/1.96 = ~30.6

46.66/1.95 = ~23.93

28/1.96 = ~14.29

21.99/1.98 = ~11.1

X = 31

X = 24

X = 14

X = 11

Sale 5:

Sold for 20 keys

Seller: https://backpack.tf/profiles/76561198086070401#!/compare/1532476800/1532649600

Buyer: https://backpack.tf/profiles/76561198060949511#!/compare/1530748800/1532649600

X = 20

Sale 6:

Sold for 17 keys + ~1 key in items

Seller: https://backpack.tf/profiles/76561198062900578#!/compare/1530316800/1530403200

Buyer: https://backpack.tf/profiles/76561198119349110#!/compare/1530316800/1530403200

X = 18

Sellers:

29 keys:

https://i.imgur.com/Ov6660e.png

https://backpack.tf/item/6478671464

35 keys:

https://i.imgur.com/z11FBpJ.png

https://backpack.tf/item/5046549228

Excluding the bot.tf purchase at ~6.5 keys because it looks like it came from a scammer.

https://backpack.tf/item/6884088099

Sales at:

11

14

18

20

24

31

31 is too high given the month unsold at 29. Excluding 31.

11 looks like an outlier, excluding 11.

Pure sales at 18 and 20. Marketplace sales that aren’t already being excluded at 14 and 24. Gonna go with a short range, giving priority to the pure sales we have. Results in the same mid-point as the large range would end up being anyways.

Going with 18-20.