Sale 1:

Sold for $33.33 on Marketplace.tf

https://marketplace.tf/items/417;5;u33

https://backpack.tf/item/1099071939

33.33/2 = ~16.7

X = 17

Sale 2:

Sold for 14 keys

Seller: https://backpack.tf/profiles/76561198349886701#!/compare/1511740800/1511827200

Buyer: https://backpack.tf/profiles/76561198420143920#!/compare/1511568000/1511827200

X = 14

Sale 3:

Sold with cheap item for 13 keys

http://www.tf2outpost.com/trade/29444430 - B/O of 14

Seller: https://backpack.tf/profiles/76561198166982558#!/compare/1511308800/1511395200

Buyer: https://backpack.tf/profiles/76561197988391296#!/compare/1511308800/1511395200

X = 13

Sale 4:

Bulk for Screaming Tiger Conga

Seller: https://backpack.tf/profiles/76561198097865584#!/compare/1507766400/1507852800

Buyer: https://backpack.tf/profiles/76561198087440842#!/compare/1507766400/1507852800

Sale 5:

Bulk for Pro. KS Aussie Rocket Launcher

Seller: https://backpack.tf/profiles/76561198087440842#!/compare/1508025600/1508112000

Buyer: https://backpack.tf/profiles/76561198102442712#!/compare/1507939200/1508025600

Sale 6:

Bulk for Grail Results

Seller: https://backpack.tf/profiles/76561198303059077#!/compare/1509753600/1509840000

Buyer: https://backpack.tf/profiles/76561198269371230#!/compare/1509753600/1509840000

Sale 7:

Bulk for Searing Towering Pillar of Hats

Seller: https://backpack.tf/profiles/76561198267466993#!/compare/1510531200/1510876800

Buyer: https://backpack.tf/profiles/76561198166982558#!/compare/1510790400/1510876800

Sellers:

15 keys:

http://www.tf2outpost.com/trade/29452760 - 1 week

Sales at:

13

14

17

Going to exclude the sale at 17 given that:

- It is a Marketplace.tf sale

- There’s a seller at 15

- There are pure sales at 13-14

- The seller most likely was not selling for 17 keys when listed on backpack.tf.

Going with 13-14.