Buying house with unpermitted garage conversion Antioch, CA

[Jarrad Henry]

Yay! My second post. (Am I a real estate investor yet?) :)

I have been getting a various opinions regarding a stellar property in Antioch CA. 

Has a nice floor plan but the garage was converted to a larger kitchen. In addition to that a permit was never pulled for the development. I haven't had any inspections done but only learned that it was unpermitted after my offer was accepted.

My realtor seems to think that it is no big issue. "More than 95%" of homes have unpermitted development. My concern is the liability.

Does a renter not have to pay rent if the a space is unpermitted? Can the city of Antioch force me to do an expensive demolition? Should I just walk away from the property?

Any help is appreciated. You guys are awesome.