All credit due:

https://backpack.tf/suggestion/5f2543a85e6b701a5a1b5828

Updating it while links are still fresh

https://marketplace.tf/items/tf2/602;5;u61

May 21: 18/1.88 = 9.5

May 23: 18/1.9 = 9.5

Jun 19: 12.05/1.98 = 6

Jul 31: 17.99/1.92 = 9.5

Sale 1:

https://backpack.tf/item/2202397216

https://backpack.tf/profiles/76561198404472674#!/compare/1578700800/1589241600

https://backpack.tf/profiles/76561198169078824#!/compare/1583020800/1591920000

untrace

Sale 2:

https://backpack.tf/item/7956654575

https://backpack.tf/profiles/76561198002757046#!/compare/1588896000/1589068800

https://backpack.tf/profiles/76561198286379108#!/compare/1571184000/1589068800

Rubi sold for 7 keys 10 ref rounding to 7 keys

By Xergoyf

https://bot.tf/stats/listings/429W7GG5

https://bot.tf/stats/listings/M19WP9X1

https://bot.tf/stats/listings/Y9QXWEJ6

Rubi sold within hours @ 7 keys 10 ref

hence, 7 is QS

Sale 3:

https://imgur.com/a/zUwOcIf (by Jam)

https://backpack.tf/profiles/76561198241557144#!/compare/1544140800/1596153600

Compare not working, going by ss. Sold for 10 keys pure

Sale 4:

https://bot.tf/stats/listings/MQ0L8VZQ

https://bot.tf/stats/listings/429G92W5

b/o capped at 9

Classifieds:

https://imgur.com/a/TpMn41k

Only seller for 8 keys been listed for 3 days, will wait and see if it sells.

6 and 7 is excluded, range at 9-10