By the way, if you ever want to sell a cruel knife, use this sales pitch that I just made up:
Take a level 125 rogue. Give it radiant earthstone bp and legs, obsidian gloves and boots, 250 damage fiery axe, 70 damage veteran helm, spectral reaper ring, three godly firefang rings, spectral midnight talisman, grand sunfire charm of venom, and cruel knife. Two poisoners bracelets of dexterity, even better. Stack full dex with a little bit of vit because strength doesn't increase elemental damage and you have low piercing damage. Max poison weapon, shadowstrike, life steal, etc.
That makes 670 heat damage, 100 magic damage, and 60 poison damage (+100 with reaper ring buff) at a blazingly fast speed, for a total of 830 elemental damage (930 with reaper ring buff). Include the damage boost from poison weapons and you could easily see yourself dealing up to 1k damage per hit.
Now you pop a hero haste lix. Just guessing, that puts you at maybe 5 hits per second?
Imagine a rogue, serving up 5k damage a second. That, people, is the definition of DPS.
And that's why I'm selling a cruel knife for <insert insanely high price here>.
In reality, though, a cruel knife can be farmed from Dustwither Catacombs or even the deeper end of Crookback. It is not insanely rare; it's just that it is mind-numbingly boring to farm in a low level area.