If I join the Dark Brotherhood and start murdering people am I going to incur a penalty in the thieves guild? I am the Gray Fox of the thieves guild but I dont wanna have to pay 1000 gold to get back into the guild that I run.
Getting Kicked from Dark Brotherhood:
If you kill, steal, or attack any members before the... event will result in a Kick, you'll need to do a special quest to retain your membership.
Getting kicked from The Thieves Guild:
If you kill or attack during a mission ( Once you actually attempt to do the mission, like enter the specific quest zone it will take its effect ), You'll be required to pay about 1000 gold to rejoin the guild, I believe it goes up in value every time you break the rules.