Using past 2 months.

Sale #1:

https://backpack.tf/profiles/76561198425919113#!/compare/1550275200/1550880000

Untraceable.

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Sale #2:

https://backpack.tf/profiles/76561198021055079#!/compare/1551657600/1551744000

Bought for 6 keys.

6 keys

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Sale #3:

https://backpack.tf/profiles/76561198002757046#!/compare/1550880000/1550966400

Sold for 7 keys.

7 keys

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Sale #4:

https://backpack.tf/profiles/76561198021055079#!/compare/1550448000/1550534400

Sold for a Fountain of Delight Taunt: Square Dance (12 keys). B/O was 10 keys.

10 keys

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Sale #5:

https://marketplace.tf/items/1168;5;u3019

Sold for $19.99.

$19.99 / $1.80 = ~11 keys

11 keys

Sales:

6, 7, 10, 11. Going with 7 - 10 keys, buyer at 6 keys. Unsold @ 10 keys for 4 months.