The Thieves Guild
Thievery is hard work.  Not only the actual stealing and pick pocketing, but also selling the loot without getting caught.
That's where Thief Guilds come in.  The thief can comfortably fence his stolen goods and brag about his deeds at the guild.  Its mottos is "Thou shall not steal here".  Hey, even the sleazy have some honor.

Spielburg's thief guild is competing with the brigands for business.  The brigands take anything outside the city, the thieves everything inside.  To steal inside Spielburg you need to be a member of the guild, which of course includes a fee.  Plus you'll have to buy a lockpick or toolkit if you don't have one.  You can rob two houses in the town: the sheriff's house and the old lady's home.  Both places have loot to fence at the guild, so it's worth joining.  Plus, you can practice your throwing by playing Dag-Nab-It with the Chief.  If you're good you can make money!  To find the guild you'll need to make the thief sign to some fellow thieves and they'll tell you the password, or as Crusher says it "passwoid".

There is no organized Thieves Guild in Shapeir, but Dinarzad will be willing to fence things for you.
She'll need a sign, of course, or else her guard Franc will make a quick end of you.  Just ask her about a job and she'll give you some work.

A house the thief can break into and steal things from.

In Raseir Signor Ferrari is the Thieves Guild.  He's after the blackbird, and he sends you after it.
One of the sneakiest thieves in the series, you definitely have to watch your back around Ferrari.

Tarna is a bad land for thieves.  Just look at this one who was caught.  He's begging on the streets for food.
If a thief is caught s/he becomes honorless and no one is allowed to interact with him/her.
This is especially bad in times of war when caravans are few and far between,
making the honorless one starve in the city for a long time.  Needless to say there's no thieves guild in Tarna.
There is, however, someone who can give you some tips.  The rope maker knew some thieves in his early years,
so he can teach you some helpful skills.

You can steal from the drummer if you're clever enough, and you can help the warring tribes by
breaking into their leaders' huts and returning some items, but other than that there's nothing to steal.

Mordavia's Thieves Guild has been inactive ever since the members died or were transformed.
Since the swamps have closed off the valley there have been less places to steal from,
so some of the members decided to go to the castle.
No one returned, so now there's only you and the Chief, and the Chief isn't feeling himself lately.
He has been transformed into a giant bug, and it would be in your best interest to help him.
You can learn how to disarm traps here, using the Acme Mark II Toolkit, the latest in thieving technology.
Though you can't fence anything, the Chief tells you where you can rob places, mainly Nikolai's house, the burgomeister's office, the monastery, and the castle.

Silmaria has a thriving Thieves Guild now that the king is dead.  The assassin who killed the king also killed the Chief Thief in hopes of becoming the new one.  You can enter the Chief Thief contest along with five other contestants: Ferrari, Ugarte, Nawar, the cloaked man, and a mystery contestant (some say Gnome Ann).  The winner will be the one who pays the most money or who brings in the black bird.

You can practice your skills in the guild, whether it be disarming traps or pickpocketing, a new skill.
You can fence hot items from a few houses, and can boast about robbing the bank.  Arrestes is the operating fence, he's the one who will sell you important supplies.

Meet some notable thieves

On to the supplies