Sales on marketplace:

Unusual: https://marketplace.tf/items/tf2/463;5;u3014

Keys: https://marketplace.tf/items/tf2/5021;6

1.

My sale, 7 July, https://backpack.tf/item/6313202361

Sold for $83.99, keys are $1.99

83.99/1.99 = 42.21 Keys

2.

6 May

Sold for $80, keys were $1.89

80/1.89 = 42.33 Keys

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1. https://backpack.tf/profiles/76561198087099341#!/compare/1593993600/1593907200

Untraceable

2. https://backpack.tf/profiles/76561198114325442#!/compare/1578355200/1592524800

Untraceable

3. https://gyazo.com/0ae1e6cd5bce27f17b887e176c479d2a

Proof: https://gyazo.com/7d1427263c5fbfc1be49f314248eb628

I bought it for 31 Keys

4. https://backpack.tf/item/6313202361

https://backpack.tf/profiles/76561198203811797#!/compare/1593475200/1593561600

https://backpack.tf/profiles/76561198126770721#!/compare/1592524800/1593561600

Untraceable

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(42.21 + 42.33 + 31)/3

= 38.51 Keys