I believe that if you go back down to the first level, you will find a trapdoor into the basement. If you go down there, I think (IIRC) that there is a secret door down there that leads to the sewers. This allows you to avoid the flaming fist guards. You *will*, however, have to fight the guards on the first floor. I don't believe that whacking those guys affected my reputation.
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Now where did I leave that doughnut?!