Sale 1: Bulk.

https://backpack.tf/profiles/76561198147511179#!/compare/1553385600/1553731200

https://backpack.tf/profiles/76561198165055074#!/compare/1553299200/1553385600

Sale 2: High/Untrace.

https://backpack.tf/profiles/76561198165055074#!/compare/1553558400/1553644800

https://backpack.tf/profiles/76561197970775310#!/compare/1553558400/1553644800

Sale 3: Bulk.

https://backpack.tf/profiles/76561197970775310#!/compare/1553731200/1553817600

https://backpack.tf/profiles/76561198047941585#!/compare/1553731200/1553817600

Sale 4: ~16 Keys.

Sold For The Dead Head (15.25) + Dead of Night (0.46) = 15.71 keys.

https://backpack.tf/profiles/76561198047941585#!/compare/1554768000/1554854400

https://backpack.tf/profiles/76561198087524152#!/compare/1554508800/1554854400

Sale 5: Untrace.

https://backpack.tf/profiles/76561198087524152#!/compare/1554854400/1555027200

https://backpack.tf/profiles/76561198830633436#!/compare/1554854400/1554940800

Sale 6: Untrace/Bulk.

https://backpack.tf/profiles/76561198830633436#!/compare/1555200000/1556928000

https://backpack.tf/profiles/76561198841365001#!/compare/1556755200/1556928000

Marketplace.tf Sales:

https://marketplace.tf/items/30874;5;u121

Sale 7: ~14 Keys.

Mar 23

$25.20 / $1.81 = 13.92 keys

Sale 8: ~16 Keys.

Mar 28

$27.99 / $1.79 = 15.64 keys

Usable Sales: 14/16/16

Going with 14-16 keys.

Thanks to scourge for the premium!