Sale #1:

https://bot.tf/stats/listings/M0JD9WQY

https://backpack.tf/profiles/76561198363395191#!/compare/1553040000/1553126400

Bought for 7 keys and 22 ref.

7.5 keys

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Sale #2:

https://backpack.tf/profiles/76561198086990597#!/compare/1551916800/1552003200

Bulk sale.

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Sale #3:

https://backpack.tf/profiles/76561198061836787#!/compare/1552003200/1552089600

Untraceable.

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Marketplace.tf stats:

https://marketplace.tf/items/30615;5;u3019

Past 90 days:

1x $18 ($18 / $1.77 = ~10 keys)

1x $10.59 ($10.59 / $1.80 = ~6 keys)

Sales:

6, 7.5, 10. Going with 7.5 - 10 keys.