Might be a bit high but whatever, valid sales are scarce.

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Sale #1 3rd - 4th of May

http://backpack.tf/profiles/76561198046888654?time=1430711774 before

http://backpack.tf/profiles/76561198046888654?time=1430722800 after

1:1 with Aces High Waxy(~11 via mini) 11

Mini 29th - 30th of April, no 2nd sale without an outdated hat charade, so just a mini

http://backpack.tf/profiles/76561198087751174?time=1430365261

http://backpack.tf/profiles/76561198087751174?time=1430377200

Sold for 11 keys pure+5 ref, rounded down to 11. 11

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Sale #2 13th - 14th of April

http://backpack.tf/profiles/76561198055280950?time=1428908400 before

http://backpack.tf/profiles/76561198055280950?time=1428994800 after

1:1 with Steaming Gatsby (12.5) That wasn't a mini, so i'm applying overpay. 12.5*0.9 = 11.25 -> 11

~~~~~

Conclusion: Two non-pure sales for 11 keys, using 11.