Thanks to Blaze:

https://backpack.tf/item/2729362946

https://gyazo.com/d8af4323f4b849a8a06c552f23d297a9 - listed for 30k

https://backpack.tf/profiles/76561198065360678#!/compare/1637971200/1638057600

https://backpack.tf/profiles/76561198375230689#!/compare/1637971200/1638057600

(looks like aussie sticky + s. ks bottle + s. pro ks skullcutter + 3k used to buy directly/indirectly)

the 3 keys in that sale were not involved as they were used to buy the strange prof ks detonator as seen by histories making that sale 27 keys.

https://gladiator.tf/listings/61ae356c99151b66a740d2b3

https://backpack.tf/item/2729362946 - person who bought it now has it listed at 30

https://backpack.tf/item/2829059954

https://backpack.tf/profiles/76561198164651434#!/compare/1628640000/1628726400

25 keys

https://backpack.tf/profiles/76561198043458554#!/compare/1633305600/1633651200

Looks like 25 keys again

https://backpack.tf/item/2653260125

https://backpack.tf/profiles/76561198049595224#!/compare/1623801600/1630972800

Looks bulk

https://backpack.tf/profiles/76561198097200828#!/compare/1631059200/1631145600

https://backpack.tf/profiles/76561199030851597#!/compare/1631059200/1631145600

36 keys

https://backpack.tf/profiles/76561199030851597#!/compare/1631145600/1631318400

dunno

https://backpack.tf/profiles/76561198151636845#!/compare/1626998400/1631923200

i dunno

https://backpack.tf/item/2622715764

https://backpack.tf/profiles/76561198042257915#!/compare/1576022400/1632268800

https://backpack.tf/profiles/76561197995540052#!/compare/1632182400/1632355200

Untrace

https://backpack.tf/item/2521244824

https://backpack.tf/profiles/76561198154648669#!/compare/1627344000/1627430400

20 keys received matches B/O https://gladiator.tf/listings/60ff53e67dc8517e7bc78bac (now outdated)

https://backpack.tf/item/3372625309

https://backpack.tf/profiles/76561198354811369#!/compare/1630713600/1634688000

Hard to say

https://backpack.tf/profiles/76561198850274253#!/compare/1632009600/1632096000

https://backpack.tf/profiles/76561198243128080#!/compare/1632009600/1632096000

Also hard to say, could be bulk, snapshot suggests 26 keys https://gladiator.tf/listings/6147cdb26b809ba067254679

https://backpack.tf/profiles/76561198243128080#!/compare/1632960000/1633046400

Seems like bulk for Stormy Yellow Belt

SCM:

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

38.8k

40k

36.6k

Blaze:

https://steamcommunity.com/market/listings/440/Collector%27s%20Professional%20Killstreak%20Postal%20Pummeler

https://steamcommunity.com/market/pricehistory/?country=US&currency=1&appid=440&market_hash_name=Collector%27s%20Professional%20Killstreak%20Postal%20Pummeler - new sales at 22 and 31 keys

All New Sales:

20, 22, 25, 25, 27, 31, 36, 37, 39, 40

The 20k sale is now outdated, and I guess the recent 27 sale makes everything above 31 look high (I think including 31 still makes sense given 30 seller is pretty close, plus it's the second most recent sale).

22-31k.