Thieves Guild
The Thieves Guild are a shady Guild that effectively live up to their name by stealing as much coins out of your pockets as they possibly can as you get powers through them. That being said, anything else you might be capable of doing doesn't interest them at all. Blood? Keep it. Action points? Bah, go away. Coins, coins, coins, coins, coins...
Powers
Thievery
When they convince you to give them your money, they at least have the decency to tell you how to steal in the more illegal manner. That they're illegal anyway doesn't really matter at this point. You learn to pickpocket from the best clan in the city, the only with enough skill to pass it on to someone like you. Or have you seen the Splinters of Dusk or another non-Guild clan give you powers in the game? No? I didn't think so.
Shadows
The good thief does not only know how to not be noticed whilst stealing, the good thief also knows how to conceal himself whilst preparing to steal. All in the light of the Thieves Guilds, Shadows is buyable here, at a laughably cheap price that almost makes you question the Thieves Guild.
Money you leave...
The Thieves Guild will leave you alone permanently with their buttons once you've left 25 000 coins with them. It's all they ask, though.
Cormorant's Perch
Unlike other Guilds, the Thieves Guild used to have a quirk: They believed in newbie friendly, or at least, they pretended they do. They sent their first Thieves Guild up to Cormorant's Perch (the north-west corner of the city) all the time, so that it'd be easier to find for freshblood. (Not really, of course - it was just a game glitch.)
At the time, the shop Interesting Times moved into the area just as often.
The result was hellish - full squares littered the ways of newbies trying their best to fight their way through to the first Thieves Guild. They got robbed on the way by veterans, who in turn got robbed as they get stuck outside a full bank by the vampires with Surprise, who in turn managed to deposit. It was more than messy up there, and a true suicide area for any new vampires - but a feast for the long fingers for they who knew their way around and had Scrolls of Turning or Surprise.