I've reached the top rank of Thief, and decided to move onto robber. Here's the problem. I've checked the manual, gamefaqs, and GOG forums, and still don't have enough information to make it work.
I'm just trying to figure out how to start the occupation at the moment. I know how to click the Robber icon in the job list, but that's about it.
So if my understanding is correct, you need to own a castle outside of town to be a Robber. Every robber always rejects my offers to buy theirs. If I'm supposed to, say, offer double the lowest allowable offer, then I'm in trouble. I have a hard enough time getting my money to hover stably around $20-30k, even with $6k/turn for top thief. Even with kidnapping.
So, I figure, to circumvent that problem, I will send my thieve's out to attack it. I scout a castle to absolutely 100%, then order the attack. I get the message along the lines of "You can't even find the front door. Do more research next time." I cannot fathom the logic at all and have no idea what it's suggesting I do. I tried this several times, always getting that same message.
That's been my experience with Robber thus far. I'm stumped!

Another thing I haven't had luck in understanding are the Guard Houses. I read that owning them makes thievery easier, so I guess I get that much.
What I don't get is when, after taking over a guard house, there's a whole interior building with various rooms and an employee. It appears as if you should be able to do things here, but I don't know what! If there are any specific actions to perform, I can't find them. The employee doesn't seem to do anything other than wander around.
The other thing I'm confused about is the laziness of the town guard. You'd THINK attacking a guard shack and slaughtering the guards would cause at least minor upset, but not really. The city guard seems like it's saying, "Well, it's their own fault for being unprepared. Go ahead and keep it. We don't need to watch that part of town. Oh but don't sneak into anybody's house or you're in big trouble!" Burglary > multiple police homicide?

So there you have it. Any insight or help is appreciated!

Go to your house and chose new Master Profession.

Yes, I did that before making this post. The problem was the game basically said "Okay, you're a robber now." And I said "That's nice... now what?" I pretty much came to a dead end right there.

To work as a robber, you first need the appropriate profession level, and the appropriate building (same as all professions actually). To get a robber's castle, you will have to be lucky. They do every now and then go up for auction, but I'm not sure if you can influence that or not (try finding out who the owner is, challenge him to a duel and kill him if possible). This isn't so different from trying to get a Blacksmith, since by the time you decide to change professions, most of the buildable areas will have probably already been used.
Also, none of the outer city buildings can be robbed by thieves as I recall (mine, quarry, timber camp, robber castles, and maybe the palaces as well).

Now, on to the Guard House. Guard Houses work similar to the Thieves' Guild. You can assign the guards to practice, patrol, or maybe a few more things (too long since I played a guard, can't actually recall). By owning all the Guard Houses, and never sending out a patrol, your thieves will not encounter any patrols (obviously). As I recall, alt or ctrl should highlight any hotspots on the screen, though some of them are only improvements and can't be actually used.

So, tl;dr version. Guard Houses work similar to Thieves' Guilds on how to use them, and getting a Robber's Castle isn't easy.

First off: You CAN attack the robbers fortresses!
Important things to know: you have to scout it quite thoroughly before. Your thiefs should be equipped with pistols. Their Combat and stealth skills should be 6 stars. YOU should have at least 3-4 stars in the combat talent (and probably at least that much in stealth too).


Even when i attack with more than 6 thieves only 6 will show up in the fight, so theres no use in sending more. Send them out to attack the fortress. Watch your thieves on the map, shortly before they all enter the robber fortress press "Q" (Quicksave!). If they wont find the entrance just reload and try again. With all the aforementioned skills it never took me more than three tries to find the entrance and start the fight.
Good Luck :)

Your thieves actually finding the entrance depends on several factors (in my experience) and its a random decision, that gets decided again, when you reload the game. Quicksaving also works for burglaries, kidnapping and pretty much every other random event (robberies of your cart!!)
Hope i could help.