Resuggesting, all credits to The Blue Fox and The Real Slim Strange!

1) Bought one for 30 keys pure:

https://backpack.tf/profiles/76561198020981163#!/compare/1642204800/1642291200

More accurate screenshot: https://imgur.com/a/yxT1M5W

2) Previous owner bought it for 26 keys pure few days ago:

https://backpack.tf/profiles/76561198251960730#!/compare/1641859200/1641945600

(all other sales info provided by mentioned Gurus)

3) 23 keys (The Blue Fox said it was 22 keys + 15 ref, but I clearly see 23 keys transfered from EtErNaL_Bjørn to Hypno, checked all keys from EtErNaL_Bjørn's comparison (second link)):

https://backpack.tf/profiles/76561198120774019#!/compare/1638316800/1638403200

https://backpack.tf/profiles/76561198018658142#!/compare/1638316800/1638748800

4) Untraceable:

https://backpack.tf/profiles/76561198190455050#!/compare/1639353600/1639440000

https://backpack.tf/profiles/76561198120774019#!/compare/1639353600/1639440000

5) Untraceable:

https://backpack.tf/profiles/76561198120774019#!/compare/1641168000/1641254400

https://backpack.tf/profiles/76561199057164252#!/compare/1641168000/1641254400

6) Whether untraceable or extremely low or involving friends trade:

https://backpack.tf/profiles/76561199057164252#!/compare/1642204800/1642291200

https://backpack.tf/profiles/76561199139031975#!/compare/1642204800/1642291200

Summing up:

23

26

30

Taking 23-30 range