How to Negotiate Price Concessions for Unpermitted Work

[Jessica Costa]

I just finished a home inspection on a three-family I have under contract and there is a basement apartment that has recently been re-done (new walls, ceilings, kitchen, bathroom, flooring, plumbing, etc.) It is half situated on concrete slab and the other half is pretty much built on top of dirt (we think, we are unable to get to it) and I called the building department and there were no permits pulled.

How should I go about negotiating down the price? We offered full ask originally.