f it sold via paypal you will need to take the value at what keys are selling for paypal for using a 'key mini' (see most recent key suggestion on what it looks like)

Only if it sold on marketplace.tf thats when you use the key value on marketplace

Edit:

https://backpack.tf/profiles/76561198039843013#!/compare/1777248000/1777334400

https://backpack.tf/profiles/76561198033899941#!/compare/1777161600/1777334400

Nevermind sold for 75 keys pure

Fyi you just need to put other a screenshot of the steam trade or use the compare links to show what it sold. The two links I provided above show this