Just make sure you finish the quest, get the reward, THEN extort money. Might as well get the best of both worlds.
Also, you can be as rude as you want to be with the key NPCs (Aribeth, Fenthick, Desther, etc.). They'll still do everything they do for you as if you were a good guy. Just don't kill anyone in their presence.
Other evil things to do in Chapter 1:
1. Blackmail Oleff to not reveal his involvement with the Moonstone Mask.
2. Tell Bethany (the girl who hits you up to save the Peninsula district as soon as you walk out of the temple) to take a long walk off a short pier. Then talk to her again and do it again (I love the response).
3. Tell the halfling woman (forget her name) in the house right near the entrance of the Peninsula district that you could care less about what is happening.
4. Watch as the zombies rip apart the innocents in the street (if I am not mistaken, you don't get any xp for saving them, anyway).
5. If you already know the quests (i.e. have finished the game before), kill all the people who surrender, unless you need them to finish the quest.
Just a few suggestions!