Are there any unsafe areas in Venice that I should avoid when booking a place to stay?
I cannot think of any. We have spent a full month there, and I felt completely safe walking around Venice, even by myself.
We never felt uncomfortable anywhere in Venice. We wandered many "off-the-beaten-path" neighborhoods, and attended the theater late in the evening. We stayed at Hotel Flora and felt totally safe.
We never have felt unsafe in any of the areas of Venice. We have stayed in San Marco, Cannaregio( our favorite) and Dorsoduro.
Same here. Even when walking alone on quiet narrow streets in the evening, I don't feel unsafe. (You might want to edit the title to the topic instead of your name).