Sale #1:

https://backpack.tf/profiles/76561198849487866#!/compare/1551312000/1552521600

SCM Sale.

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Sale #2:

https://marketplace.tf/items/338;5;u34

Sold for $29.86.

$29.86 / $1.79 = ~17 keys

17 keys

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Sale #3:

https://backpack.tf/profiles/76561198083134207#!/compare/1550102400/1550188800

Bought for 10 keys.

10 keys

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Sale #4:

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

https://backpack.tf/profiles/76561198358778649#!/compare/1547420400/1547506800

Bought for 9 keys and 10 ref.

9 keys

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Sale #5:

https://backpack.tf/profiles/76561198162120088#!/compare/1547856000/1548028800

Sold for 12 keys.

12 keys

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Sale #6:

https://backpack.tf/profiles/76561198312480435#!/compare/1549753200/1549839600

Bought for 10 keys and 1.22 ref.

10 keys

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Sale #7:

https://backpack.tf/profiles/76561198083134207#!/compare/1550102400/1550188800

Untraceable.

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Sale #8:

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

https://backpack.tf/profiles/76561198358778649#!/compare/1553558400/1553644800

Bought for 10 keys and 21 ref.

10 keys

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Sale #9:

https://backpack.tf/profiles/76561198268798857#!/compare/1548028800/1548115200

Sold with a '72 Taunt: The Meet the Medic (~4 keys) and a Professional Killstreak Mantreads Kit (~2 keys) for an Orbiting Fire Industrial Festivizer (~12 keys).

Too low, might use for the Orbiting Fire suggestion.

Sales:

9, 10, 10, 10, 12, 17. Going with 10 - 12 keys.