https://backpack.tf/rules

2 sellers at 16 keys unsold.

Use the value of keys on the site at which the item sold to determine the key conversion at the time of the trade. (i.e. use the SCM value of keys on SCM sales, use the marketplace.tf value of keys on marketplace.tf sales, use the opskins value of keys on opskins sales). For most transactions, this means you can use the key value at the exact date of the sale.

Marketplace sales take the value of keys on the site at the time of the sale.

For example, the sale at $35.99 on September 27th would use what keys sold for on marketplace on September 27th, which was $1.87

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

https://i.imgur.com/vh2XAtu.png

35.99/1.87 = 19 keys, after rounding.

There are also a lot of recent sales to look into:

https://backpack.tf/item/13106565265

https://backpack.tf/item/12546221836

https://backpack.tf/item/10526445277

https://backpack.tf/item/4301394115

https://backpack.tf/item/4215219473

If you wanna commit to pricing items, I'd recommend looking at this guide:

https://forums.backpack.tf/topic/59832-guide-how-to-use-the-compare-function/#comment-575508