Sale 1:

Sold for Miami Nights Horrific Headsplitter

http://www.tf2outpost.com/trade/29286370 - B/O of 20

Seller: https://backpack.tf/profiles/76561198061108999#!/compare/1500681600/1500768000

Buyer: https://backpack.tf/profiles/76561198076352227#!/compare/1500681600/1500854400

Easily caps.

X = 20 (Capped by B/O)

Sale 2:

Sold for 13 keys (IDs match)

No outpost

Seller: https://backpack.tf/profiles/76561198355490842#!/compare/1504828800/1504915200

Buyer: https://backpack.tf/profiles/76561198186700182#!/compare/1504915200/1505001600

X = 13

Sale 3:

Sold for 13 keys (IDs match)

http://www.tf2outpost.com/trade/29367798 - B/O of 14

Seller: https://backpack.tf/profiles/76561198095804696#!/compare/1505347200/1505433600

Buyer: https://backpack.tf/profiles/76561198079474154#!/compare/1501027200/1505433600

X = 13

Sale 4:

Sold for Hot Well Worn Blue Mew SMG

No outpost

Seller: https://backpack.tf/profiles/76561198108148076#!/compare/1504310400/1504915200

Buyer: https://backpack.tf/profiles/76561198191881121#!/compare/1504915200/1505001600

Can be used on the SMG.

Sale 5:

Sold with 1 key for Steaming Lucky Shot

No outpost

Seller: https://backpack.tf/profiles/76561198191881121#!/compare/1504915200/1505001600

Buyer: https://backpack.tf/profiles/76561198095804696#!/compare/1504656000/1505001600

Should be used on the Lucky Shot.

Sellers:

15 keys:

https://i.imgur.com/TNQ5o0Q.png - 5 days

Sales at:

13 (2x)

20

20 is an outlier, excluding 20.

Going with 13 flat.