Sale 1:

Sold for Starstorm Slumber Wing Mann + ~12 keys in pure/aussies

http://www.tf2outpost.com/trade/29375443 - B/O of 20

Seller: https://backpack.tf/profiles/76561198205910661#!/compare/1507075200/1507161600

Buyer: https://backpack.tf/profiles/76561198334198375#!/compare/1507161600/1507248000

Easily caps.

X = 20 (Capped by B/O)

Sale 2:

Sold for 18 keys + 16 ref

http://www.tf2outpost.com/trade/29398382 - B/O of 20

Seller: https://backpack.tf/profiles/76561198231082180#!/compare/1507939200/1508025600

Buyer: https://backpack.tf/profiles/76561198324692104#!/compare/1507939200/1508025600

X = 18

Sale 3:

Sold for Blizzardy Storm Hard Counter + Bubbling Tam O’ Shanter

http://www.tf2outpost.com/trade/29367412 - B/O of 17

Seller: https://backpack.tf/profiles/76561198043160163#!/compare/1505520000/1505692800

Buyer: https://backpack.tf/profiles/76561198205910661#!/compare/1505606400/1505692800

Easily caps.

X = 17 (Capped by B/O)

Sale 4:

Sold for Haunted Ghosts Buckaroo’s Hat (Suggestion at 16.5) + cheap item

No outpost

Seller: https://backpack.tf/profiles/76561198334198375#!/compare/1507248000/1507334400

Buyer: https://backpack.tf/profiles/76561198130662205#!/compare/1507248000/1507334400

X = 17

Sale 5:

Sold for 15 keys + ~1 key in metal

Seller: https://backpack.tf/profiles/76561198119634686#!/compare/1507248000/1507334400

Buyer: https://backpack.tf/profiles/76561198072744029#!/compare/1507248000/1507334400

X = 16

Sale 6:

Sold for 15 keys + 5 ref

Seller: https://backpack.tf/profiles/76561198349886701#!/compare/1510012800/1510099200

Buyer: https://backpack.tf/profiles/76561198208814695#!/compare/1509840000/1510099200

X = 15

Sale 7:

Sold for Steaming Sultan’s + Nuts N’ Bolts Respectless Robo-Glove + Haunted Medimedes (6) in a 15 day hold

No outpost

Seller: https://backpack.tf/profiles/76561197998934095#!/compare/1507939200/1509408000

Buyer: https://backpack.tf/profiles/76561198307417466#!/compare/1507939200/1509494400

This’ll be way too high without a B/O cap.

Sale 8:

Bulk for Sulphurous Fed

Seller: https://backpack.tf/profiles/76561198145843391#!/compare/1508371200/1508457600

Buyer: https://backpack.tf/profiles/76561198067557593#!/compare/1508371200/1508457600

Haunted Ghosts Buckaroo’s Hat:

https://backpack.tf/suggestion/5a0a90e0cf6c75548f390000

Sellers:

~15.6 keys:

https://i.imgur.com/Us5D990.png - 11 days

16.2 keys:

https://i.imgur.com/Xw4lyGN.png - 3 days

17 keys:

https://i.imgur.com/WgNT5Up.png - 1 day

20 keys:

https://i.imgur.com/BdvN4hR.jpg - 1 month

Sales at:

15

16

17 (2x)

18

20

20 seems pretty high, given the current sellers. Excluding 20.

Going with 15-18.