Most of illegal construction fines I have heard of were under circumstances when the work performed was visible from the outside in plain sight. Of course, many renovations that are purely interior also need permits, such as electrical or plumbing work, or anything involving structural support.
If a remodeler chooses not to obtain proper building permits (for reasons of the bureaucratic burden etc) and (s)he never manifests signs of construction visible on the outside of the building, can municipal building inspectors obtain a court (or other form of legal) warrant to enter the property and find evidence of illegal construction for the purposes of issuing fines or injunction to cease all work?
Also, upon sale of the property, what legal channels exist whereby the illegal builder can be audited by the building inspection? I think home inspection is done by private inspectors and not municipal agents.
This is in the U.S. I understand building codes vary across the country but I'm also thinking that warrants for inspection are somehow related to the 4th Amendment.