Counter, credit to Payback/Dzaster

Sale 1 -

10 keys

https://backpack.tf/profiles/76561198331323738#!/compare/1710201600/1710201600/nearest

https://backpack.tf/profiles/76561198016593811#!/compare/1710201600/1710201600/nearest

can't find anything in seller's compare but on buyer's compare all 10 key histories show that keys went to seller

Sale 2 -

https://backpack.tf/profiles/76561198116849874#!/compare/1709596800/1709596800/nearest

https://backpack.tf/profiles/76561198331323738#!/compare/1709596800/1709596800/nearest

Unusualified

Sale 3 -

https://marketplace.tf/items/tf2/31381;5;u3005

$15, April 5th

https://backpack.tf/item/14268300182 - probably this one

https://marketplace.tf/items/tf2/5021;6 - keys were $1.65

15/1.65 = ~9.1, rounds to 9

https://backpack.tf/item/14268300182 - history shows it went to STN, but we can’t tell what they paid.

Sellers:

https://stntrading.eu/item/tf2/Unusual+Fountain+of+Delight+Taunt%3A+Neck+Snap

https://imgur.com/a/VtCGGrS

https://backpack.tf/item/14268300182 - ~20 keys

Sales at:

9

10

STN purchase is untraceable. Their current price suggests they paid ~11 keys (though their buy price was drastically higher 3 months ago before they got it.

Taking 9-10 keys.