Sale 1:

Sold with Strange Invis Watch (~5) for Time Warp Milkman (Suggestion at 50)

Seller: https://backpack.tf/profiles/76561198113488534#!/compare/1550534400/1550620800

Buyer: https://backpack.tf/profiles/76561198139189194#!/compare/1549756800/1550620800

https://backpack.tf/item/7530245238

X = 45

Sale 2:

Sold for 39 keys

Seller: https://backpack.tf/profiles/76561198066956277#!/compare/1543363200/1543449600

Buyer: https://backpack.tf/profiles/76561198056793444#!/compare/1543363200/1543449600

https://backpack.tf/item/7341725686

X = 39

Other Sales:

https://backpack.tf/item/6629651277 (#1-3)

#1

Untraceable

https://backpack.tf/profiles/76561198072306525#!/compare/1550534400/1550620800

https://backpack.tf/profiles/76561198177759574#!/compare/1550534400/1550620800

#2

Untraceable

https://backpack.tf/profiles/76561198177759574#!/compare/1550534400/1550620800

https://backpack.tf/profiles/76561198093824611#!/compare/1550534400/1550620800

Only 25 keys and some other items match, though I can guarantee that more than 25 keys were involved.

#3

Untraceable

https://backpack.tf/profiles/76561198093824611#!/compare/1550620800/1550707200

https://backpack.tf/profiles/76561198156365397#!/compare/1527465600/1550707200

Time Warp Milkman:

https://backpack.tf/suggestion/5c74d7326780720acc41511a

Sellers:

https://i.imgur.com/cQdN59z.png

https://backpack.tf/item/7341725686 - 60 keys

https://backpack.tf/item/7530245238 - 60 keys

https://backpack.tf/item/6253990423 - 60 keys

https://backpack.tf/item/5848860134 - 65 keys

Sales at:

39

45

Going with 39-45.