When trying to get this achievement, you should avoid any quests or actions that may give you mercy or charity points such as refusing money for rewards, offering to help Kiri for free, assisting the ghost near the spider queen boss, etc. These points will go against the "evil points".
Here is how I got the achievement.
poison the guild of steel for demon pact - 1 evil point.
help the man get rid of wife's body - 1 evil point.
Haggle with the merchants sword quest- 1 evil point.
haggle wth the merchant for spider queen quest - 1 evil point.
told zaar about the catacombs - 1 evil point.
(Karma: 2 cruelty, 3 greed at ths point)
Accept the quest to recover the reaper sword. Slay the man for the sword - this quest counts as 2 cruelty points rather than one.
Agree to help Kiri for a price (You may not be able to do this with Jesker). - 1 evil point (greed).
At this point you should have 4 cruelty and 4 greed without any mercy or charity.
If you have followed everything to this point, you will be forced to return to Thole to warn them about the Nomads. However, before doing so, pick up the new quests from the merchant. Inform him of his dead man and aks for an additional reward for an additional greed point.
Kill the scorpian king for the merchant and demand seven fifty for compensation. At this point, the achievement should pop. You will end wth 4 cruelty and 6 greed. If you previously messed up and earned a mercy or charity point, you will need to obtain 10 more evil points than the good points that you have. You can gain more evil points later on by helping Kiri slay Tiberius and by giving the Wolf Shaman Staff to the mages instead of the miners.