https://marketplace.tf/items/30658;5;u35

https://backpack.tf/item/7361436441 <-- Prolly Dec 17 sale

https://backpack.tf/item/6923206639 <-- Dec 27 or Dec 28 sale

Sales at 15, 20, 21

Sale at 15 happened on Dec 28 what means that on Dec 27 there wasn't this listing (or it was listed after someone had bought one for 20 keys). So 15 must've sold in 1 day, means quicksale

https://backpack.tf/profiles/76561198041108750#!/compare/1544486400/1544572800

17 keys

https://backpack.tf/profiles/76561198262258500#!/compare/1544572800/1544745600

Nothing matches

https://backpack.tf/profiles/76561198045730256#!/compare/1544313600/1544572800

16 keys, IDs match

https://backpack.tf/profiles/76561198337734785#!/compare/1545868800/1545955200

https://backpack.tf/profiles/76561198119149660#!/compare/1545868800/1545955200

Looks like nothing matches

https://backpack.tf/profiles/76561198203221120#!/compare/1541116800/1541203200

https://backpack.tf/profiles/76561198371168595#!/compare/1540684800/1541203200

Using there

Creds Shuffle for these:

Sold for a Blizzardy Storm Hermes + 2 Keys = will fit

https://backpack.tf/profiles/76561198182795337#!/compare/1543363200/1543449600

Sold for a Voltaic Hat Protector Universal Translator (15) + 2 Keys + CAPPER (~2 Keys) = 19 keys

https://backpack.tf/profiles/76561198159252325#!/compare/1543449600/1543536000

Current sellers/buyers:

https://imgur.com/Wq5dOue

Sales we got:

15, 16, 17, 19, 20, 21

Taking current sellers, I'd personally exclude 20 and 21 keys sales

15 was quicksale

16 and 17 and 19 sales left so that's our range

Woah, I almost forgot how to do these