It's like eating anywhere else and people need to remember that. I would say that Italy has a more socially-important food culture, so the odds of a bad restaurant are lower overall - but they are higher in the areas where tourists tend to concentrate.
It'd be like coming to Maine and expecting decent seafood anywhere you go. That might be true if you're up north of MDI or somewhere else that tourists don't go, but there are going to be some seasonal seafood dumps waiting to rip off tourists as you get closer to places like Bar Harbor, Portland, etc. (and even then, like a lot of Italy, I do think we have an overall lower percentage of bad restaurants mostly due to a strong food culture but also because summer is only 3 months and you can't scare off the locals).
As we've said in other threads, avoid recommendations from your concierge and other tourism industry people. They'll just send you to their other friends in the tourism business.