Sale 1-4:

https://marketplace.tf/items/tf2/31048;5;u58

$34.99 / $1.78 = 19.66 keys

$13.3 / $1.75 = 7.60 keys

$19.99 / $1.71 = 11.69 keys

$13.22 / $1.70 = 7.78 keys

https://backpack.tf/item/8080409191

Sale 5:

untrace

https://backpack.tf/profiles/76561198125791160#!/compare/1579910400/1579996800

https://backpack.tf/profiles/76561198142163280#!/compare/1580860800/1581379200

Sale 6:

6 keys

https://backpack.tf/profiles/76561198142163280#!/compare/1580860800/1581379200

https://backpack.tf/profiles/76561198307532189#!/compare/1580169600/1581379200

Sale 7:

untrace

https://backpack.tf/profiles/76561198257977681#!/compare/1584144000/1584230400

https://backpack.tf/profiles/76561198053252981#!/compare/1584144000/1584230400

Sale 8:

SCM

https://backpack.tf/profiles/76561198053252981#!/compare/1584230400/1584316800

https://backpack.tf/profiles/76561198116095622#!/compare/1584057600/1584576000

Sale 9:

untrace

https://backpack.tf/profiles/76561198219377359#!/compare/1581033600/1581120000

https://backpack.tf/profiles/76561198341171690#!/compare/1581033600/1581120000

Sale 10:

bulk

https://backpack.tf/profiles/76561198219377359#!/compare/1581379200/1581465600

https://backpack.tf/profiles/76561198859721638#!/compare/1581292800/1581379200

Sale 11:

untrace

https://backpack.tf/profiles/76561198859721638#!/compare/1584144000/1584230400

https://backpack.tf/profiles/76561198271442469#!/compare/1583971200/1584230400

Sale 12:

5 keys? maybe something missing

https://backpack.tf/profiles/76561198343273185#!/compare/1584230400/1584316800

https://backpack.tf/profiles/76561198271442469#!/compare/1584230400/1584316800

==============================================================================

Sales:

6, 7.5, 8, 12, 20

buyers at 7.3: https://imgur.com/a/RrscUeO

3 months unsold at 15 keys: https://imgur.com/a/bbVjl2g

excluding 7.5 as very close to buyers