Sale 1:

https://backpack.tf/profiles/76561198928421771#!/compare/1593561600/1593648000 - 9 Keys.

https://backpack.tf/profiles/76561198068585202#!/compare/1593475200/1593648000

Sale 2:

https://marketplace.tf/items/tf2/1119;5;u3022

Jun 3 - $15 / $1.96 = 7.65 keys = 7.5 keys, couldn't find a b/o

Jun 25 - $11.25 / $1.99 = 5.65 keys = 5.5 keys, couldn't find a b/o

Sale 3, 4:

Shuffle Spy:

https://backpack.tf/profiles/76561198305676157#!/compare/1592870400/1593043200 - 9 Keys

The person who paid 9 here dumped it for 5.5 Keys a day later, so both can be excluded.

https://imgur.com/a/X2UknVZ - Another sale at 6.5 Keys. The buyer in sale 1 here dumped for 4.5 Keys, so I'd exclude both of those as well.

https://backpack.tf/profiles/76561198305676157#!/compare/1589407200/1589493600 - 6.5 Key sale comparison

6.5 - 7.5 Keys will work.