Using last month.

Sale 1:

Sold for $19.90 on marketplace.tf

https://marketplace.tf/items/30761;5;u3005 (couldn’t find the item’s history)

http://manicbot.me/keyprice/?at=2018-07-28 – 19.9/1.99 = 10

X = 10

Sale 2:

Sold for 8 keys + 11 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1532649600/1533254400

Buyer: https://backpack.tf/profiles/76561198042018679#!/compare/1533168000/1533254400

Most, if not all, the ref can be found in the buyer’s compare link. The 8 keys can be found in the seller’s end.

https://backpack.tf/item/6749647824

https://i.imgur.com/Hj01T7K.png

X = 8.5

Sale 3:

Sold for 7 keys

Seller: https://backpack.tf/profiles/76561198151484641#!/compare/1532304000/1532390400

Buyer: https://backpack.tf/profiles/76561198394267379#!/compare/1531872000/1532908800

https://backpack.tf/item/4965035823

X = 7

Sale 4:

Sold to a bot for 5 keys

Seller: https://backpack.tf/profiles/76561198097816819#!/compare/1534032000/1534118400

Buyer: https://backpack.tf/profiles/76561198363395191#!/compare/1534032000/1534118400

https://backpack.tf/item/5206121930

X = 5

Untraceable bot.tf trades:

https://bot.tf/stats/item?def=30761&q=5&ef=Fountain+of+Delight&craft=1&aus=0&ks=0

https://i.imgur.com/Hj01T7K.png

https://backpack.tf/profiles/76561198158294758#!/compare/1532649600/1532908800

https://backpack.tf/profiles/76561198305676157#!/compare/1532563200/1532649600

https://backpack.tf/item/6749647824 - 5 keys and 13.11 ref according to bot.tf, nothing matches here.

Sellers:

10 keys:

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

https://backpack.tf/item/5409214767

Sales at:

5

7

8.5

10

5 is too low, and is a single sale to a quickbuyer, excluding.

10 is too high, given the month unsold at 10. Excluding 10.

Going with 7-8.5.