Sale 1:

Sold for Bubbling Electric Escorter (9.5) + <1 key in items

Seller: https://backpack.tf/profiles/76561198262763716#!/compare/1493683200/1493769600

Buyer: https://backpack.tf/profiles/76561198128578694#!/compare/1493596800/1493769600

X = 10

Was used in the escorter suggestion, but can be used here as it wasn’t dependent on the sale to set a low or high end there. Also, it would be more suitable here anyways, as items were added with the escorter.

Sale 2:

Sold for 9 keys

Seller: https://backpack.tf/profiles/76561198153782854#!/compare/1493683200/1495497600

Buyer: https://backpack.tf/profiles/76561198080757395#!/compare/1493510400/1493683200

X = 9

Sale 3:

Quicksold for 9 keys

Seller: https://backpack.tf/profiles/76561198080757395#!/compare/1493683200/1493769600

Buyer: https://backpack.tf/profiles/76561198262763716#!/compare/1493683200/1493769600

X = 9

Sellers:

10 keys:

http://i.imgur.com/a4yGFyX.png - 7 days

https://backpack.tf/u/76561198159855421

http://www.tf2outpost.com/trade/29273105

http://i.imgur.com/E8RwsaS.png - 5 months

https://backpack.tf/u/76561198061376237

http://www.tf2outpost.com/trade/29228837

11 keys:

http://i.imgur.com/FkjAzeR.png - 6 months

https://backpack.tf/u/76561198006544512

http://www.tf2outpost.com/trade/28925582

Sales at:

9 (2x)

10

5 month old seller at 10 shows that the item cannot sell at 10. Excluding 10.

Going with 9 flat.