First suggestion, thanks to Jarool for the help ^^

Sold for Haunted Ghosts Airdog (23) + 9 keys

http://www.tf2outpost.com/trade/28833470 - Deleted B/O

Seller: https://backpack.tf/profiles/76561197987183850#!/compare/1494720000/1495324800

Buyer: https://backpack.tf/profiles/76561198155106081#!/compare/1495238400/1495324800

X = 32

Sold for 27 keys (key histories in the buyer’s compare link) in about 2 days

http://www.tf2outpost.com/trade/28887806 - B/O of 27

Seller: https://backpack.tf/profiles/76561198080179568#!/compare/1492819200/1492905600

Buyer: https://backpack.tf/profiles/76561198042569903#!/compare/1492732800/1492905600

X = 27

Sold for 23 keys to a quickbuyer

Seller: https://backpack.tf/profiles/76561198042569903#!/compare/1493164800/1493251200

Buyer: https://backpack.tf/profiles/76561198073553007#!/compare/1493078400/1493164800

X = 23

Sold for 22 keys + 1 ref to an unusual bot

Seller: https://backpack.tf/profiles/76561198044474683#!/compare/1493856000/1493942400

Buyer: https://backpack.tf/profiles/76561198304138933#!/compare/1493856000/1493942400

X = 22

Sold for 22 keys? (probably wrong here)

http://www.tf2outpost.com/trade/28846341 - B/O of 27

Seller: https://backpack.tf/profiles/76561198073553007#!/compare/1491177600/1491264000

Buyer: https://backpack.tf/profiles/76561198266300577#!/compare/1491177600/1491264000

Sold to a bot for 19 keys

Seller: https://backpack.tf/profiles/76561198012938128#!/compare/1496188800/1496534400

Buyer: https://backpack.tf/profiles/76561198311820950#!/compare/1496448000/1496534400

X = 19

Sold with 6 keys + 15 ref for Blizzardy Storm Thirst Blood (Outdated)

Seller: https://backpack.tf/profiles/76561198095429386#!/compare/1496880000/1498262400

Buyer: https://backpack.tf/profiles/76561198089572069#!/compare/1496880000/1497398400

Might be better to use this sale on the thirst blood, but given its current sellers, I think it would end up being an outlier regardless of whether it gets used here or on the thirst blood

Bulk for Terror-Watt Antlers

Seller: https://backpack.tf/profiles/76561198126204929#!/compare/1492646400/1492732800

Buyer: https://backpack.tf/profiles/76561198096545860#!/compare/1492646400/1492732800

Should be used on the antlers

Untracable, cannot be used here

Seller: https://backpack.tf/profiles/76561198096545860#!/compare/1492732800/1492905600

Buyer: https://backpack.tf/profiles/76561198080179568#!/compare/1492819200/1492905600

Bulk for Nebula Universal Translator

Seller: https://backpack.tf/profiles/76561198266300577#!/compare/1495843200/1495929600

Buyer: https://backpack.tf/profiles/76561198125791160#!/compare/1495756800/1495843200

Bulk

Seller: https://backpack.tf/profiles/76561198125791160#!/compare/1496188800/1496275200

Buyer: https://backpack.tf/profiles/76561198121050731#!/compare/1496016000/1496275200

Bulk, untraceable

Seller: https://backpack.tf/profiles/76561198044474683#!/compare/1493337600/1493856000

Buyer: https://backpack.tf/profiles/76561198028179754#!/compare/1493683200/1493856000

Bulk, unusable

Seller: https://backpack.tf/profiles/76561198028179754#!/compare/1493856000/1493942400

Buyer: https://backpack.tf/profiles/76561198044474683#!/compare/1493856000/1493942400

Untracable

Seller: https://backpack.tf/profiles/76561198304138933#!/compare/1493856000/1493942400

Buyer: https://backpack.tf/profiles/76561198177251270#!/compare/1489622400/1494201600

Sold to a bot

Seller: https://backpack.tf/profiles/76561198243530442#!/compare/1497657600/1497744000

Buyer: https://backpack.tf/profiles/76561198296062531#!/compare/1497571200/1497657600

Sellers at 25 and 26:

https://i.imgur.com/hJegH7I.png

Unable to tell how long the seller at 25 has been selling for.

Sales at 19 and 22 went to quickbuying bots. Excluding 19 and 22.

Sale at 23 went to a known quickbuyer. Excluding 23.

Sale at 32 looks like an outlier, given the current sales and sellers. Excluding 32.

Going with 26-27.

Helpful criticism is welcome ^-^