Sale #1:

https://bot.tf/stats/item?def=338&q=5&ef=Circling+TF+Logo&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198316961222#!/compare/1550876400/1550962800

Bought for 12 keys and 22 ref.

12 keys

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Sale #2:

https://bot.tf/stats/item?def=338&q=5&ef=Circling+TF+Logo&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198312480435#!/compare/1549666800/1549753200

Bought for 12 keys and 18 ref

12 keys

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Sale #3:

https://backpack.tf/profiles/76561198066057807#!/compare/1549584000/1549670400

Untraceable.

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Sale #4:

https://bot.tf/stats/item?def=338&q=5&ef=Circling+TF+Logo&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198312480435#!/compare/1550012400/1550098800

Sold for 14 keys and 22 ref.

14 keys

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Sale #5:

https://bot.tf/stats/item?def=338&q=5&ef=Circling+TF+Logo&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198305494036#!/compare/1550271600/1550358000

Bought for 12 keys and 20 ref.

12 keys

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Sale #6:

https://backpack.tf/profiles/76561198129749194#!/compare/1548547200/1548633600

Sold with a Strange Face Full of Festive (5.4 keys) for a Searing Plasma Peacenik's Ponytail (19 keys)

No minis available on the Peacenik's Ponytail.

14 keys

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Sale #7:

https://backpack.tf/profiles/76561198066586338#!/compare/1548547200/1548633600

Sold for 15 keys.

15 keys

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Sale #8:

https://backpack.tf/profiles/76561198227756380#!/compare/1548806400/1548892800

Bulk / Untraceable.

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Sale #9:

https://backpack.tf/profiles/76561197963292494#!/compare/1551139200/1551225600

Untraceable.

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Sale #10:

https://backpack.tf/profiles/76561198232041512#!/compare/1552262400/1552348800

Bulk.

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Sale #11:

https://backpack.tf/profiles/76561198232041512#!/compare/1553299200/1553385600

Sold for 15 keys.

15 keys

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Sale #12:

https://marketplace.tf/items/338;5;u11

Sold for $29.99.

$29.99 / $1.79 = ~17 keys

17 keys

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Sale #13:

https://marketplace.tf/items/338;5;u11

Sold for $22.

$22 / $1.79 = ~12 keys

12 keys

Sales:

12, 12, 12, 12, 14, 14, 15, 15, 17. 12 is too common to ignore, going with 12 - 15 keys.