Purchasing a property with rehab done without permits

[Jacob Carlson]

Hey BiggerPockets! 

I am in the midst of doing my due diligence on a quad. 

Here's the situation.  There is an off-market quad that I want to house hack.  The building was built in 1888. The current owner/seller has completely rehabbed two units including plumbing, electrical, windows and aesthetics.  One unit was not upgraded but still has a breaker box and everything is in working order.  The last unit, the one I would occupy, is in the middle of being rehabbed.  They will finish it enough to make it livable and then I will finish it from there. 

The issue is the current owner/seller did not pull any permits for this, but had it done by licensed contractors. I am concerned that this may come back to bite me in the future.  Here are some of my questions:

1. Am I protected in anyway since I am not the one that did the unpermitted work? Or is the risk transferred to me?

2. What is the risk involved if I decide to move forward and purchase this property?

3. I am thinking about finishing the basement myself which would require a permit. If I get it permitted and inspected does that open all the other renovations up to question and possibly opening a can of worms? 

4. Am I overthinking this or would/should this be a deal breaker?

Thank you in advance for your advice!