Thanks to Shuffle for the freebie and the previous suggestor as I am borrowing evidence from them.

Sale #1: $24.99 / $1.79 (https://manic.tf/keyprice/?at=2020-08-17) = 13.96 ~ 14 keys

https://backpack.tf/item/8417574376

~~~~~~~~~~~~~~~~~~~~~~~

Item tracing on the Sale #1:

Sale #2

untraced/SCM

https://backpack.tf/profiles/76561198228227148#!/compare/1592179200/1592265600

https://backpack.tf/profiles/76561198088878793#!/compare/1592265600/1592352000 (missing)

~~~~~~~~~~~~~~~~~~~~~~~

Sale #3

traced 6 keys - QS to bot

https://backpack.tf/profiles/76561198088878793#!/compare/1592265600/1592352000 (ID: 8908109215)

https://backpack.tf/profiles/76561198334598690#!/compare/1592265600/1592352000

~~~~~~~~~~~~~~~~~~~~~~~

Sale 1 (Thanks to ⚡Fumino Furuhashi⚡) is capped at buyout of 11 keys (Thanks to Shuffle)

https://imgur.com/a/aytHsxW

http://webcache.googleusercontent.com/search?q=cache:b1iXldG5194J:https://marketplace.tf/items/tf2/30874;5;u58&hl=en&gl=us&strip=1&vwsrc=0

11 flat.