Sale 1:

Sold for ~15 keys in items

http://www.tf2outpost.com/trade/29231728 - No B/O

Seller: https://backpack.tf/profiles/76561198267189538#!/compare/1498694400/1498780800

Buyer: https://backpack.tf/profiles/76561198053175174#!/compare/1498780800/1499126400

X = 15

Sale 2:

Sold for Strange Spec. KS Shooting Star (7) + ~4 keys in items

No outpost

Seller: https://backpack.tf/profiles/76561198170592025#!/compare/1496620800/1496707200

Buyer: https://backpack.tf/profiles/76561198140317722#!/compare/1496534400/1496707200

X = 11

Sale 3:

Sold for Steaming Nano (9.5) + taunt (~0.5)

No outpost

Seller: https://backpack.tf/profiles/76561197963500354#!/compare/1496966400/1497052800

Buyer: https://backpack.tf/profiles/76561198132292727#!/compare/1496707200/1497225600

X = 10

Sale 4:

Sold for Green Confetti Mongolian (9.5) + cheap cosmetic

No outpost

Seller: https://backpack.tf/profiles/76561198329540909#!/compare/1502668800/1502755200

Buyer: https://backpack.tf/profiles/76561198129499386#!/compare/1502668800/1502755200

Seller at 8.3 on the Mongolian. Probably better to value this sale at 9.

X = 9

Sale 5:

Sold for > 9 keys in items

http://i.imgur.com/tMQGjr1.png - B/O was probably 9.

Seller: https://backpack.tf/profiles/76561198164651434#!/compare/1496448000/1496534400

Buyer: https://backpack.tf/profiles/76561198170592025#!/compare/1496448000/1496534400

X = 9

Sale 6:

Sold for 8 keys + 13 ref (ID’s match)

http://www.tf2outpost.com/trade/28882978 - B/O of ~8.7

Seller: https://backpack.tf/profiles/76561198056472266#!/compare/1496620800/1496793600

Buyer: https://backpack.tf/profiles/76561198341047875#!/compare/1494460800/1496707200

X = 8

Sale 7:

Bulk for a strange unusual flamethrower

Seller: https://backpack.tf/profiles/76561198051925253#!/compare/1496188800/1496275200

Buyer: https://backpack.tf/profiles/76561198041902665#!/compare/1496188800/1496275200

Sellers:

9 keys:

http://i.imgur.com/yk4iPUm.png - 1 month

10 keys:

http://i.imgur.com/pmYecTu.png - 7 days

http://i.imgur.com/ShKqirx.jpg - 1 month

http://i.imgur.com/DAXuU9N.png - 4 months

11 keys:

http://i.imgur.com/lIJKrjz.png - 5 months

Sales at:

8

9 (2x)

10

11

15

11 and 15 are outliers, given the unsolds. Excluding 11 and 15.

8 is also an outlier, given the buyers at and higher than 8. Excluding 8.

10 has multiple aged sellers, and given the month old seller at 9, I’d say that 10 should be excluded. Excluding 10.

Going with 9 flat.