https://steamcommunity.com/market/pricehistory/?country=US&currency=1&appid=440&market_hash_name=Collector%27s%20Pain%20Train

Feb 3, ~25.1 keys

Feb 26, ~68 keys

Mar 22, ~47 keys

https://steamcommunity.com/market/pricehistory/?country=US&currency=1&appid=440&market_hash_name=Collector%27s%20Specialized%20Killstreak%20Pain%20Train

Feb 12, ~22.9 keys

May 18, ~18.7 keys

https://steamcommunity.com/market/pricehistory/?country=US&currency=1&appid=440&market_hash_name=Collector%27s%20Professional%20Killstreak%20Pain%20Train

Jun 9, ~50 keys

https://backpack.tf/item/2560510629

https://backpack.tf/profiles/76561199059160806#!/compare/1654214400/1654300800

https://backpack.tf/profiles/76561198017977884#!/compare/1654300800/1654387200

https://gladiator.tf/time-machine?item=Collector%27s+Professional+Killstreak+Pain+Train&at=2022-06-03T12%3A30%3A00.000Z

This most likely sold for 33 keys, the Collectors Sydney sold for 50 https://gladiator.tf/time-machine?item=Collector%27s+Professional+Killstreak+Sydney+Sleeper&at=2022-06-04T03%3A26%3A00.000Z, ~4 keys leaving go to Golden Glimmer Party Trick, from the remaining 30 keys received, ~3 keys go to the Creepy Crawlies Jumping Jack https://gladiator.tf/time-machine?item=Creepy+Crawlies+Taunt%3A+The+Jumping+Jack&at=2022-06-04T18%3A23%3A00.000Z, taking 33

https://gladiator.tf/time-machine?item=Collector%27s+Professional+Killstreak+Pain+Train&at=2022-06-11T22%3A01%3A00.000Z

Seller at 40 (previously ~33), buyer at 20

Credits Blaze:

https://backpack.tf/profiles/76561197961272955#!/compare/1656979200/1657065600

https://backpack.tf/profiles/76561199059160806#!/compare/1656979200/1657065600 - sold for 20 keys

https://backpack.tf/profiles/76561199230237260#!/compare/1656633600/1656892800

https://backpack.tf/profiles/76561197961272955#!/compare/1656547200/1656979200 - sold for 40 keys (dumped for the 20 above)

https://backpack.tf/profiles/76561199066855627#!/compare/1655683200/1655769600

https://backpack.tf/profiles/76561198408606810#!/compare/1655683200/1655769600 - sold for 3 skins for Aurora Polaris Taunt: Bucking Bronco + spelled Strange Specialized Killstreak Shotgun (will be below buy-orders)

https://steamcommunity.com/market/pricehistory/?country=US&currency=1&appid=440&market_hash_name=Collector%27s%20Pain%20Train - new sale at 25~ keys

https://steamcommunity.com/market/pricehistory/?country=US&currency=1&appid=440&market_hash_name=Collector%27s%20Specialized%20Killstreak%20Pain%20Train - new sale at 32~ keys

the sale at 23 keys you mentioned was already 4 months old at the time of this suggestion and therefore outdated. 25 - 33 would be better here.