Finding sales for flies hats is always so hard (no one wants them). <.< The current sellers on Outpost don't seem to be getting any bites, either. Alas, I've provided 3 sales, and 3 unusable sales (why not?). Well then...

Sale #1 (February 19th):

Slug > 1 bud + Strange Huntsman (4.4 keys; 0.32 buds after overpay)

Outpost trade:

http://www.tf2outpost.com/trade/25105344

Buyer's inventory:

http://backpack.tf/profiles/76561198055539654?time=1420531200 -> http://backpack.tf/profiles/76561198055539654?time=1424505600

Item histories:

Huntsman: http://backpack.tf/item/97215730

Bud: http://backpack.tf/item/97215730

1.3 buds

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Sale #2 (February 8th):

Slug > Ace's High Tippler's Tricorne (1.3) + Bill's Hat (3 keys; 0.25 buds) + 2 keys (0.166 buds)

Outpost trade:

http://www.tf2outpost.com/trade/24969283

Seller's inventory:

http://backpack.tf/profiles/76561198147450568?time=1423209600 -> http://backpack.tf/profiles/76561198147450568?time=1423382400

(1.3 + 0.25) * 0.9 = 1.395

1.395 + 0.166 = 1.56

1.6 buds

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Sale #3 (January 4th):

Slug > 18 keys (1.24 buds)

Outpost trade:

http://www.tf2outpost.com/trade/24351803

Inventory screenshot:

http://i.imgur.com/5uF520V.png

1.2 buds

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Unusable sales:

Sale (February 6th):

Slug > 15+ keys + ?

Outpost trade:

http://www.tf2outpost.com/trade/24822406

Buyer's inventory:

http://backpack.tf/profiles/76561198147450568?time=1423123200 -> http://backpack.tf/profiles/76561198147450568?time=1423209600

I had a lot of difficulty tracking this sale. The Pro Strange Original looks like it was sold here: http://www.tf2outpost.com/trade/24966534 resulting in an extra 12 or more keys on top of the 3 keys in the user's inventory. We can say this sale was at least 1.3 buds, but probably not more than 1.6 buds. This should fall within the range, either way.

Untrackable sale

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Sale (December 27th):

Slug > 1 bud + ?

Outpost trades:

Slug: http://www.tf2outpost.com/trade/24208510 1.4 bud B/O

Bud: http://www.tf2outpost.com/trade/24242308

Buyer's inventory:

http://backpack.tf/profiles/76561198087099341?time=1419148800 -> http://backpack.tf/profiles/76561198087099341?time=1419667200

Second bud was most likely split into keys before trade. Hard to say.

Untrackable sale

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Sale (December 1st):

Slug > Flies Attendant (1.3) + 2 keys + ~1 key in items

Outpost trade:

http://www.tf2outpost.com/trade/23803622 (all items were mentioned in comments)

This sale was a bit old, but I felt there weren't enough sales.

1.3 * 0.9 = 1.17

1.17 + 0.219 = 1.389

1.4 buds

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Mini-Suggestions:

Massed Flies Attendant:

http://www.tf2outpost.com/trade/24814458 ~1.3 bud B/O at 4 weeks

http://www.tf2outpost.com/trade/25124257 quick-sold for 15-17 keys (~1.3 buds)

http://www.tf2outpost.com/trade/24934603 quick-sold for 16 keys (~1.3 buds)

Not a whole lot else I could find. 1.3 buds may or may not be accurate.