Sale #1:

https://backpack.tf/profiles/76561198079955710#!/compare/1551657600/1551744000

Sold for 20 keys.

20 keys

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Sale #2:

https://bot.tf/stats/item?def=1157&q=5&ef=Poisonous+Bubbles+of+Regret&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198314211872#!/compare/1548198000/1548284400

Bought for 16 keys.

16 keys

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Sale #3:

https://marketplace.tf/items/1157;5;u3019

Sold for $59.99.

$59.99 / $1.80 = ~33 keys

33 keys