Challenge 19, Team F.L.A.M.B.E.S!

2nd suggestion, made by Mikey!

Sale 1:

https://marketplace.tf/items/tf2/30844;5;u3015

Unable to find item history.

Apr 7th - $45.00

Keys were $1.69, so 45 / 1.69 = 26.63, rounding to 27 keys.

Sale 2:

https://marketplace.tf/items/tf2/30844;5;u3015

https://backpack.tf/item/6277094246

Apr 28th - $48.00

Keys were $1.82, so 48 / 1.82 = 26.37, rounding to 26 keys.

Sale 3:

https://marketplace.tf/items/tf2/30844;5;u3015

https://backpack.tf/item/6264569650 - Probably this one.

May 1st - $48.00

Keys were $1.85, so 47 / 1.85 = 25.41, rounding to 25 keys.

Sale 4:

https://backpack.tf/profiles/76561197998642621#!/compare/1589500800/1589587200

https://backpack.tf/profiles/76561198335791307#!/compare/1589500800/1589587200

25 Pure

Sale 5:

https://backpack.tf/profiles/76561198073386321#!/compare/1586822400/1586908800

https://backpack.tf/profiles/76561198335791307#!/compare/1586822400/1586908800

Untrace

Classies

1 for sale at 29 for >5 months.

25-27 keys.