Despite being criminals, those in the Old Camp do have some laws. Try not to be seen breaking them. If you aren't seen you can act with impunity.
Housebreaking
The first thing you'll discover is that you can't go into most huts. The exceptions are the huts of named characters. Most named characters (such as Diego) don't care about you entering their houses, so you can rob them in broad daylight. The named characters who do mind about this can be robbed when they are in the house when you enter (even if you wake them up in the process). No-name characters can be robbed if nobody sees you enter, or if you knock them down first (more on that later). As a general rule, if you hear "hey you!" simply leave and try a different approach or come back later.
Fights
Second, if you draw your weapon within the camp everyone will react. They won't attack unless you attack first, however. As a general rule you can attack any unnamed character without punishment (attacking named characters will often result in the guards attacking you). Guards are invulnerable as are many named NPCs, and they will remain so until their role in the plot is finished.
A handful of no-name NPCs are under the protection of the guards, so attacking them will earn you a crossbow bolt in the neck; if you get shot at simply run away for a while and both the guards and your victim will forget all about it. Diggers are a sure bet as only a couple of them are protected, and the guards will just watch and laugh as you beat them into the dust. You can attack the protected diggers without problems as long as the guards are offscreen.
With your standard attacks you can't kill anybody, only knock them down, and except for protected NPCs nobody will care who you beat up. Your victim will drop their weapon and stay down for a while, and you can take their weapon and loot their prone body without anybody caring. If you kill them with a coup de grâce (use attack while standing over their prone body) you'll be in big trouble. It's best not to kill anybody as you may break a quest by doing so. Giving them a sound beating has no repercussions as they forget soon after you leave the area; except in a few cases you can beat even named NPCs and they'll treat you as a friend when you return later. Also, if you wait for them to be completely healed you can beat them over and over for experience.
Note that if you get knocked down the person who finished you will take a percentage of your Ore! If you get finished with magic or an arrow or bolt you'll die. To avoid this you can save before, and maybe consider storing some of your Ore in the vacant house Guy tells you about.
When your victim gets up he might be angry but he won't attack you, and he's weak and weaponless anyway. Those who ran away or you only wounded may resume attacking you when you next see them, but that shouldn't be a problem either. If a wounded victim flees for the castle don't pursue him too close; sometimes the guards will start shooting at you. You can just wait until he returns to finish him off.
Since a hut's owner is often the first to accost you if you enter it, knocking him down first often means you can run in and loot it. If he gets up and challenges while you're picking the chest just hit him again and re-enter the house. Remember to save before picking chests to conserve your supply of picklocks.
The Arena
There is an arena in town. You can fight there as part of the status quest involving Diego and Thorus. Note that when you fight in the arena every NPC in the nearby area comes to watch (even the guard in front of the locked door), and they stay standing there for a while after the fight is over. You can quickly lose a fight and then go rob a couple of houses with nobody around to stop you. Repeat as necessary.