Using last month.

Sale 1:

Sold for 10 keys + 40 ref

Seller: https://backpack.tf/profiles/76561198454615761#!/compare/1558483200/1558569600

Buyer: https://backpack.tf/profiles/76561198108935953 (keeps using fallback, so I can’t get a compare right now)

https://backpack.tf/item/5370848230

X = 11

Sale 2:

Sold for 10 keys

Seller: https://backpack.tf/profiles/76561198335791307#!/compare/1556236800/1556323200

Buyer: https://backpack.tf/profiles/76561198293915597#!/compare/1556323200/1556409600

https://backpack.tf/item/5370848230

X = 10

Sale 3:

Sold to a bot for 8 keys + 3 ref

Seller: https://backpack.tf/profiles/76561198446606701#!/compare/1558569600/1558656000

Buyer: https://backpack.tf/profiles/76561198802465612#!/compare/1558656000/1558742400

https://backpack.tf/item/6701365783 (not a bot.tf user)

X = 8

Sale 4:

Sold for 8 keys

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1558137600/1558224000

Buyer: https://backpack.tf/profiles/76561198844249356#!/compare/1557964800/1558224000

https://backpack.tf/item/5390417630

https://i.imgur.com/EQWvHUg.png - bot.tf confirms

X = 8

Marketplace Sales:

https://marketplace.tf/items/30840;5;u3003

$23 on 26th April

$10.11 on 30th April, excluding as it’s gonna be lower than bp.tf quickbuyers.

$23 on 2nd May

https://manic.tf/keyprice/?at=2019-04-26 - $23 / $1.79 = 12.85 keys

https://manic.tf/keyprice/?at=2019-05-02 - $23 / $1.82 = 12.64 keys

X = 13 (2x)

Other Sales:

https://backpack.tf/item/5443568715 (#1 & #2)

https://backpack.tf/item/5373185812 (#3)

https://backpack.tf/item/5355902194 (#4)

https://backpack.tf/item/5354539574 (#5)

https://backpack.tf/item/5370848230 (#6)

https://backpack.tf/item/5390417630 (#7)

https://backpack.tf/item/7434609267 - not unusual at the time

https://backpack.tf/item/5360253925 - not unusual at the time

https://backpack.tf/item/5781785710 - deposited to marketplace

https://backpack.tf/item/5374574460 - tf2mart and tradeit

#1

Untraceable

https://backpack.tf/profiles/76561198873165470#!/compare/1556496000/1556582400

https://backpack.tf/profiles/76561198454615761#!/compare/1556409600/1556496000

https://i.imgur.com/EQWvHUg.png - labelled as 7 keys + 19.11 ref (~7.5 keys)

Seller dumped a bunch of unusual taunts to the buyer, so key counting isn’t gonna be too easy here. Also, I’m certain the seller is a scammer alt lol

#2

Untraceable

https://backpack.tf/profiles/76561198454615761#!/compare/1556496000/1556582400

https://backpack.tf/profiles/76561198055432130#!/compare/1556755200/1556841600

doesn’t even show up as a sale on bot.tf

#3

Untraceable

https://backpack.tf/profiles/76561198171094499#!/compare/1557619200/1557964800

https://backpack.tf/profiles/76561198396322888#!/compare/1557878400/1557964800

https://i.imgur.com/EQWvHUg.png - labelled as 8 keys + 2 ref (~8 keys)

#4

Untraceable

https://backpack.tf/profiles/76561198058505702#!/compare/1556236800/1556582400

https://backpack.tf/profiles/76561198454615761#!/compare/1556496000/1556582400

https://i.imgur.com/EQWvHUg.png - happened around the same time as #1, but there’s only one recording of a purchase on this item around this time. Both are untraceable, so it doesn’t matter too much anyway I guess.

#5

Untraceable

https://backpack.tf/profiles/76561198147095274#!/compare/1556668800/1557360000

https://backpack.tf/profiles/76561198454615761#!/compare/1557273600/1557360000

#6

Untraceable

https://backpack.tf/profiles/76561198293915597#!/compare/1557532800/1557619200

https://backpack.tf/profiles/76561198454615761#!/compare/1557532800/1557619200

https://i.imgur.com/EQWvHUg.png - Labelled as 8 keys + 0.22 ref (~8 keys)

#7

Untraceable

https://backpack.tf/profiles/76561198067598194#!/compare/1557964800/1558137600

https://backpack.tf/profiles/76561198305676157#!/compare/1557964800/1558051200

https://i.imgur.com/EQWvHUg.png - labelled as 7 keys + 12 ref (~7 keys)

Sellers:

https://i.imgur.com/m3IUlAz.png

https://backpack.tf/item/5373185812 - ~8.75 keys

https://backpack.tf/item/5354539574 - ~9.15 keys

https://backpack.tf/item/6701365783 - ~10.5 keys

https://backpack.tf/item/5367124813 - 11 keys

Sales at:

8 (2x)

10

11

13 (2x)

With 4 sellers at 11 and cheaper, excluding the higher sales is gonna be a bit of a stretch. Excluding 13 (both marketplace sales), and 11.

Going with 8-10.