Sale 1:

https://backpack.tf/profiles/76561198116928217#!/compare/1566777600/1566864000

https://backpack.tf/profiles/76561198056176130#!/compare/1566691200/1566864000

Sold for 11 keys

Sale 2:

https://backpack.tf/profiles/76561198167637295#!/compare/1565049600/1565136000

https://backpack.tf/profiles/76561198341171690#!/compare/1565049600/1565136000

QS

sale 3:

https://backpack.tf/profiles/76561198337734785#!/compare/1568246400/1568332800

https://backpack.tf/profiles/76561198262993846#!/compare/1568246400/1568332800

https://backpack.tf/profiles/76561198089253101#!/compare/1568246400/1568332800

Untrace

sale 4:

https://backpack.tf/profiles/76561198050518375#!/compare/1567468800/1567555200

https://backpack.tf/profiles/76561198281630040#!/compare/1567728000/1567814400

https://backpack.tf/profiles/76561198080179568#!/compare/1567728000/1567814400

Untrace then QS

Sale 5:

https://backpack.tf/profiles/76561198080179568#!/compare/1568246400/1568332800

https://backpack.tf/profiles/76561198880384227#!/compare/1568073600/1568764800

untrace

sale 6:

https://backpack.tf/profiles/76561198050518375#!/compare/1567468800/1567555200

https://backpack.tf/profiles/76561198817631515#!/compare/1567382400/1567555200

Sold for 6 keys

sale 7:

https://backpack.tf/profiles/76561198817631515#!/compare/1569628800/1569974400

https://backpack.tf/profiles/76561198331838737#!/compare/1569888000/1569974400

Bulk

sale 8:

https://backpack.tf/profiles/76561198331838737#!/compare/1570147200/1570320000

https://backpack.tf/profiles/76561198063640894#!/compare/1570147200/1570233600

Bulk

Sale 9:

https://backpack.tf/profiles/76561198063640894#!/compare/1570492800/1570665600

https://backpack.tf/profiles/76561198080179568#!/compare/1570665600/1570752000

untrace

sale 10, 11:

https://marketplace.tf/items/tf2/254;5;u34

$14.94 / $1.80 = 8.30 keys

$13 / $1.82 = 7.14 keys

Total sales @:

6, 7, 8.5, 11 keys

seller for 7 keys, unsold for nearly 2 weeks,

sellers on MPTF for ~8 keys, four of em.

buyers up to ~5.5 keys,

note that 11 key sale was an outlier as it seems to have been bought for the spell,

let's hesitantly take 6 - 7 keys.