Resuggestion, thanks to K1ng for the info!

Sale 1:

https://backpack.tf/profiles/76561198311498888#!/compare/1534809600/1534896000

https://backpack.tf/profiles/76561198050414618#!/compare/1534896000/1534982400

Sold for 30 keys + 5 ref (ID Match)

Sale 2:

https://backpack.tf/profiles/76561198055437713#!/compare/1532217600/1532736000

https://backpack.tf/profiles/76561198258504512#!/compare/1532217600/1532304000

Sold for 29 keys

Sale 3:

https://backpack.tf/profiles/76561198258504512#!/compare/1532995200/1533081600

https://backpack.tf/profiles/76561198072725528#!/compare/1532822400/1533081600

Bulk.

Sale 4:

https://backpack.tf/profiles/76561198072725528#!/compare/1533600000/1533686400

https://backpack.tf/profiles/76561198410760897#!/compare/1533600000/1533686400

Bulk, then QS to bot.

Sale 5:

https://backpack.tf/profiles/76561198313538268#!/compare/1534204800/1534291200

https://backpack.tf/profiles/76561198041030261#!/compare/1533945600/1534291200

Untrace.

Sale 6:

https://backpack.tf/profiles/76561198079294342#!/compare/1534550400/1534723200

https://backpack.tf/profiles/76561198045679387#!/compare/1534636800/1534723200

Can only trace 10 keys

Sale 7:

https://backpack.tf/profiles/76561198045679387#!/compare/1535414400/1535500800

https://backpack.tf/profiles/76561198260716834#!/compare/1535500800/1535587200

Untrace.

Sale 8:

https://marketplace.tf/items/152;5;u8

Sold for 56 USD

Keys at 1.98,

Total is 28.28 keys

Total sales @:

28, 29, 30.

Not including duped as rules state. (because, by my rationale, the hat must be worth less 30 keys before dupes can be included.

K1ng's Part:

Recent sale at ~35 keys on marketplace:

https://marketplace.tf/items/152;5;u8

https://bot.tf/stats/item?def=152&q=5&ef=Haunted+Ghosts&craft=1&aus=0&ks=0 ----- looks like there are sales at 33, 34, 35 and 37, but are a pain to trace.

Can't say if the marketplace sale was for the dupe or not, but given the bot.tf sales I would use it and go with 28-35 here.

Taking 28 - 35 keys