Sale 1: Untrace.

https://backpack.tf/profiles/76561198052373313#!/compare/1587254400/1587340800

https://backpack.tf/profiles/76561198374186859#!/compare/1581292800/1588809600

Sale 2: Untrace.

https://backpack.tf/profiles/76561198052373313#!/compare/1587340800/1587427200

https://backpack.tf/profiles/76561198090393125#!/compare/1583884800/1588204800]

Sale 3: Untrace.

https://backpack.tf/profiles/76561198052373313#!/compare/1586822400/1586908800

https://backpack.tf/profiles/76561198135394914#!/compare/1586908800/1587945600

Sale 4: ~8 Keys Pure. (Calling )

https://backpack.tf/profiles/76561198306530692#!/compare/1585785600/1585872000

https://backpack.tf/profiles/76561198113899098#!/compare/1585785600/1585872000

Sale 5: Untrace.

https://backpack.tf/profiles/76561198113899098#!/compare/1586044800/1586217600

https://backpack.tf/profiles/76561198317420068#!/compare/1586217600/1587340800

Sale 6: ~3.85 Keys. (QS)

https://manic.tf/keyprice/?at=2020-04-06&price=6.5 - Apr 6

$6.5 / $1.69 = 3.85 keys - No B/O

Sale 7: ~19 Keys.

https://marketplace.tf/items/tf2/30673;5;u3036 - Apr 13

$33.33 / $1.72 = 19.38 keys - No B/O

Sale 8: ~19 Keys.

https://marketplace.tf/items/tf2/30673;5;u3036 - Apr 15

$33.99 / $1.77 = 19.20 keys - No B/O

Sale 9: ~23 Keys.

https://marketplace.tf/items/tf2/30673;5;u3036 - Apr 17

$39.99 / $1.77 = 22.59 keys - No B/O

Sale 10: ~22 Keys.

https://marketplace.tf/items/tf2/30673;5;u3036 - Apr 20

$39.99 / $1.79 = 22.34 keys - No B/O

Sale 11: ~25 Keys.

https://marketplace.tf/items/tf2/30673;5;u3036 - Apr 21

$44.99 / $1.79 = 25.13 keys - No B/O

Sale 12: ~15 Keys.

https://marketplace.tf/items/tf2/30673;5;u3036 - Jun 12

$30 / $2.00 = 15.00 keys = 25.13 keys - No B/O

Sale 13: ~25 Keys.

https://marketplace.tf/items/tf2/30673;5;u3036 - Jun 26

$49.99 / $2.03 = 24.63 keys keys - No B/O

Sales: 3.85/8/15/19/19/22/23/25/25

Going with 15-25 keys.

Credits to ＣＨＲＩＳ, ✪Wrein Needs MEDIC GF❤