Sale 1:

Sold for DBD Rubber Glove (18)

No outpost

Seller: https://backpack.tf/profiles/76561198050211982#!/compare/1509580800/1509667200

Buyer: https://backpack.tf/profiles/76561198383839204#!/compare/1509580800/1509667200

X = 18

Sale 2:

Sold with 4 keys for Mallard Belgian Detective

No outpost

Seller: https://backpack.tf/profiles/76561198156315732#!/compare/1508198400/1508284800

Buyer: https://backpack.tf/profiles/76561198354296433#!/compare/1508112000/1508284800

Not using here without knowing the B/O

Sale 3:

Sold for Mallard Slick + ~2 keys in items

User doesn’t list B/O’s on outpost

Seller: https://backpack.tf/profiles/76561198011321852#!/compare/1510358400/1510444800

Buyer: https://backpack.tf/profiles/76561198090947239#!/compare/1510444800/1510531200

Again, not using without B/O

Sale 4:

Bulk for Death at Dusk Wet Works

Seller: https://backpack.tf/profiles/76561198063887625#!/compare/1507852800/1507939200

Buyer: https://backpack.tf/profiles/76561198160856661#!/compare/1507852800/1507939200

Sale 5:

Bulk for Green Black Hole Luchadore

Seller: https://backpack.tf/profiles/76561198070143554#!/compare/1509235200/1509321600

Buyer: https://backpack.tf/profiles/76561198011321852#!/compare/1509235200/1509321600

Sellers:

20 keys:

http://www.tf2outpost.com/trade/29452441 - 1 week

~19.8 keys:

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

https://backpack.tf/item/5366631842 - 47 days

Sales at:

18

The two mallard sales would end up being countered by the sellers for cheaper.

Going with 18 flat.