Sale 1:

Sold for 20 keys?

Seller: https://backpack.tf/profiles/76561198312583107#!/compare/1534550400/1534636800

Buyer: https://backpack.tf/profiles/76561198042454491#!/compare/1520985600/1534636800

https://backpack.tf/item/6315138402

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

20 keys appear together, with no visible previous owner. The buyer hasn’t had their backpack scanned in a while, as shown in the compare link, suggesting they bought the keys from the mann co store.

X = 20

Sale 2:

Sold for 20 keys + nametag

Seller: https://backpack.tf/profiles/76561198187168478#!/compare/1529452800/1529712000

Buyer: https://backpack.tf/profiles/76561198144715814#!/compare/1529539200/1529625600

https://backpack.tf/item/2791207811

X = 20

Sale 3:

Sold for 19 keys + some metal to scrap.tf

Seller: https://backpack.tf/profiles/76561198181662107#!/compare/1535068800/1535155200

Buyer: https://backpack.tf/profiles/76561198135388328#!/compare/1535068800/1535155200

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

X = 19

Sale 4:

Sold for 18 keys

Seller: https://backpack.tf/profiles/76561198042454491#!/compare/1534982400/1535068800

Buyer: https://backpack.tf/profiles/76561198181662107#!/compare/1534982400/1535068800

X = 18

Sale 5:

Sold to a bot for 16 keys

Seller: https://backpack.tf/profiles/76561198125791160#!/compare/1532563200/1532649600

Buyer: https://backpack.tf/profiles/76561198312583107#!/compare/1532563200/1532649600

https://backpack.tf/item/6315138402

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

X = 16

Sale 6:

Sold with 2 keys for Logo Vintage Tyrolean

No outpost

Seller: https://backpack.tf/profiles/76561198307532189#!/compare/1529366400/1529452800

Buyer: https://backpack.tf/profiles/76561198187168478#!/compare/1529366400/1529452800

https://backpack.tf/item/2791207811

Seems pretty high here, and would probably be low on the Tyrolean.

Untraceable sales:

#1

Untraceable, sold to scrap

https://backpack.tf/profiles/76561198036445124#!/compare/1530057600/1530144000

https://backpack.tf/profiles/76561198135388328#!/compare/1529971200/1530057600

#2

Untraceable? scrap.tf sale involving a scorching archer’s sterling

https://backpack.tf/profiles/76561198135388328#!/compare/1527724800/1527811200

https://backpack.tf/profiles/76561198106460992#!/compare/1527724800/1527811200

https://backpack.tf/item/2791207811

#3

Untraceable, sold to scrap

https://backpack.tf/profiles/76561198106460992#!/compare/1527811200/1527897600

https://backpack.tf/profiles/76561198135388328#!/compare/1527724800/1527811200

https://backpack.tf/item/2791207811

#4

Untraceable, bought from scrap.tf

https://backpack.tf/profiles/76561198135388328#!/compare/1528243200/1528329600

https://backpack.tf/profiles/76561198004386287#!/compare/1528243200/1528329600

https://backpack.tf/item/2791207811

#5

Sold to scrap

https://backpack.tf/profiles/76561198004386287#!/compare/1528502400/1528848000

https://backpack.tf/profiles/76561198135388328#!/compare/1528761600/1528848000

https://backpack.tf/item/2791207811

#6

Bought from scrap.tf for ~18 keys

https://backpack.tf/profiles/76561198135388328#!/compare/1529280000/1529366400

https://backpack.tf/profiles/76561198307532189#!/compare/1529280000/1529366400

https://backpack.tf/item/2791207811

Sellers:

~20.3 keys: (scrap.tf)

https://i.imgur.com/irAzR1K.png

https://backpack.tf/item/6315138402

Sales at:

16

18

19

20 (2x)

Bots buying at 16: https://i.imgur.com/jn0DAiL.png

Not excluding the scrap sales, or the sales lower than the scrap sales, as it has been dumped on scrap.tf way too many times.

Going with 18-20.