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Sale 1: Sold for 20 keys

http://backpack.tf/profiles/76561198084528020/#!/compare/1456560000/1456646400

Sold within a day, not using this sale.

Sale 2: Sold for 21 keys

http://backpack.tf/profiles/76561198035579290/#!/compare/1454832000/1454918400

Sale 3: Sold for Purple Confetti Armored Authority[18 keys via mini]

http://backpack.tf/profiles/76561198127850098/#!/compare/1459036800/1459296000

Since sale 1 sold within a day, I'm calling this sale an outlier.

Sale 4: Sold for Miami Nights Fed-Fightin' Fedora[30 keys via mini]

http://backpack.tf/profiles/76561198127850098/#!/compare/1458284400/1458370800

Sale 5: Sold for Haunted Ghosts Magistrate's Mullet[23.5 keys via mini]

http://backpack.tf/profiles/76561198131997294/#!/compare/1456560000/1456646400

23.5 rounding to 24 keys

Mini on Authority: http://backpack.tf/vote/id/56fc4bd7c4404503db0771f4

Mini on Fedora: http://backpack.tf/vote/id/56fc4df286674770de182efb

Mini on Mullet: http://backpack.tf/vote/id/56fc510283de6b0c2936afaf

Seller at 29 keys https://gyazo.com/2d561c737bc1e312cc11f51db450084b.png

So I have sales at 18, 20, 21, 24, and 30. 18 seems to be an outlier since 20 sold within a day. 30 seems to be too high due to a seller at 29 keys for a month. Making this a range of 21-24 keys.