This took too much time. But there are many pure sales, so no problem.

Sale 1

Sold for 33 keys

http://backpack.tf/profiles/76561198136883260#!/compare/1471910400/1472428800

No Outpost trade

=======> 33 keys

======================================================

Sale 2

No idea.

http://backpack.tf/profiles/76561198137200746#!/compare/1472601600/1472688000

http://backpack.tf/profiles/76561198131569943#!/compare/1472601600/1472688000

http://www.tf2outpost.com/trade/28456436 ----- B/O was 35 keys

=======> Not using

======================================================

Sale 3

Bulk for Secret Viewfinder

http://backpack.tf/profiles/76561198051476520#!/compare/1471737600/1471824000

http://www.tf2outpost.com/trade/28417862 ----- B/O was 40 keys

=======> Not using

======================================================

Sale 4

Sold for 28 keys

http://backpack.tf/profiles/76561198105733892#!/compare/1471824000/1471910400

No Outpost trade

=======> 28 keys

======================================================

Sale 5

Quicksold for 35 keys

http://backpack.tf/profiles/76561198125791160#!/compare/1467763200/1467849600 (sort by time)

http://www.tf2outpost.com/trade/28315764 ----- B/O was 35 keys

=======> 35 keys (qs)

======================================================

Sale 6

Quicksold for 26 keys

http://backpack.tf/profiles/76561198045354273#!/compare/1467676800/1467849600

http://www.tf2outpost.com/trade/28319393 ----- B/O was 26 keys

=======> 26 keys (qs)

======================================================

Sale 7

Sold for a duped Hearts Larrikin (mini at 23) + 10 keys + Genuine PKS Machina (~2)

http://backpack.tf/profiles/76561198045354273#!/compare/1469491200/1469577600

http://www.tf2outpost.com/trade/28349299 ----- B/O was 34 keys

----------------------------------------------

Mini for the Larrikin: Can't find an usable sale for the duped one. Seller for 23, taking 23.

http://www.tf2outpost.com/trade/28452355

----------------------------------------------

=======> 23 + 10 + 2 = Capped at 34 keys

======================================================

Sale 8

Quicksold for 26 keys

http://backpack.tf/profiles/76561198133029091#!/compare/1469577600/1469750400

No Outpost trade. Owner had it for ~4 days

=======> 26 keys (qs)

======================================================

Sale 9

Sold for 35 keys

http://backpack.tf/profiles/76561198125791160#!/compare/1471737600/1471824000 (sort by time)

No Outpost trade

=======> 35 keys

======================================================

Sellers

- http://www.tf2outpost.com/trade/28439958 ----- 35 keys

- http://www.tf2outpost.com/trade/28451424 ----- 34 keys

- http://www.tf2outpost.com/trade/28448852 ----- 33 keys

Summary

- Sales for 26 (qs), 26 (qs), 28, 33, 34, 35 (qs), 35.

Going with 33-35 keys. 28 happened off the market and is close to 26, which is a quicksale point. 33-35 range includes the most recent, full-pure sales as well as current sellers.

Criticism appreciated!