~Zerckatz.

Sale 1: Untrace/Bulk.

https://backpack.tf/profiles/76561198106657658#!/compare/1554940800/1555459200

https://backpack.tf/profiles/76561198047941585#!/compare/1555372800/1555459200

Sale 2: Untrace.

https://backpack.tf/profiles/76561198928347702#!/compare/1557100800/1557187200

https://backpack.tf/profiles/76561198199425379#!/compare/1557100800/1557187200

Sale 3: ~12 Keys.

Sold For Strange Professional Killstreak Flare Gun (3) + Strange Professional Killstreak Festive Axtinguisher (3) + Strange Professional Killstreak Degreaser (6).

(6+3+3=12)

https://backpack.tf/profiles/76561198081907770#!/compare/1552089600/1552176000

https://backpack.tf/profiles/76561198063026437#!/compare/1552089600/1552348800

Sale 4: ~15 Keys.

Sold For Holy Grail Taunt: The High Five! (15)

https://backpack.tf/profiles/76561198248296912#!/compare/1552953600/1553040000

https://backpack.tf/profiles/76561198418740133#!/compare/1552953600/1553040000

Sale 5: Bulk.

https://backpack.tf/profiles/76561198418740133#!/compare/1553299200/1553385600

Sale 6: Untrace/Low.

https://backpack.tf/profiles/76561198139656272#!/compare/1552953600/1553040000

https://backpack.tf/profiles/76561198135299063#!/compare/1552953600/1553212800

Sale 7: Untrace.

https://backpack.tf/profiles/76561198135299063#!/compare/1556236800/1556323200

https://backpack.tf/profiles/76561198305676157#!/compare/1556236800/1556323200

Sale 8: Untrace.

https://backpack.tf/profiles/76561198305676157#!/compare/1557014400/1557100800

https://backpack.tf/profiles/76561198059701300#!/compare/1557014400/1557273600

Sale 9: Low/Untrace.

https://backpack.tf/profiles/76561198106175567#!/compare/1557100800/1557187200

https://backpack.tf/profiles/76561198312265776#!/compare/1557100800/1557187200

Sale 10: ~14 Keys Pure.

https://backpack.tf/profiles/76561198312265776#!/compare/1557273600/1557360000

https://backpack.tf/profiles/76561198101623903#!/compare/1557273600/1557360000

Sale 11: ~15 Keys Pure.

https://backpack.tf/profiles/76561198042847664#!/compare/1554681600/1554768000

Sale 12: Untrace.

https://backpack.tf/profiles/76561198168863803#!/compare/1551916800/1552003200

https://backpack.tf/profiles/76561198071995863#!/compare/1551830400/1552003200

Marketplace.tf Sales:

https://marketplace.tf/items/167;5;u3005

Sale 13: ~20 Keys.

Mar 21, 19

$35.00 / $1.79 = 19.55 keys

Sale 14: ~17 Keys.

Apr 14, 19

$29.99 / $1.77 = 16.94 keys

https://bot.tf/stats/item?def=167&q=5&ef=Fountain+of+Delight&craft=1&aus=0&ks=0

https://gyazo.com/208beb5f05605cb49ebf1884cc2581f8

1 @ 13 keys

1 @ 14 keys, 40.00 ref

1 @ 15 keys

Sales: 12/13/14/14/15/15/17/20

Going With 13-17 (Thank's to shuffle)