Sale #1:

https://backpack.tf/profiles/76561198077721723#!/compare/1548806400/1549152000

Untraceable.

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Sale #2:

https://backpack.tf/profiles/76561198070703103#!/compare/1548892800/1548979200

Bought for 4 keys and 16 ref.

4.5 keys

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Sale #3:

https://backpack.tf/profiles/76561198259986634#!/compare/1552608000/1552694400

Bought for 4 keys and 20 ref.

4.5 keys

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Sale #4:

https://bot.tf/stats/item?def=1119&q=5&ef=Poisonous+Bubbles+of+Regret&craft=1&aus=0&ks=0

https://backpack.tf/profiles/76561198305676157#!/compare/1551913200/1551999600

Sold for 4 keys and 22 ref.

4.5 keys

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Sale #5:

https://backpack.tf/profiles/76561198259986634#!/compare/1552435200/1552521600

Sold with ~4.5 keys of sweets for a Subatomic A Head Full of Hot Air (10.5 keys)

6 keys

Sales:

4.5, 4.5, 4.5, 6. Going with 4.5 - 6 keys.