At least that is my experience in my market, where almost everything is 60+ years old and has un-permitted illegal work.If you just want to close on time with minimal hassle?

Investigate moving the lot line to put the house entirely on 1 property.

The house has a basement that has been built out to be, what I assume, was an illegal 2nd apt. 

The amount of ideologically inspired nonsense online is mind-boggling. 

Quote from @Chris Hertig: We recently purchased a multi-family property and have someone living illegally in an uninhabitable, detached garage. 

So ultimately this may require a discussion with counsel, and you may have to settle on splitting the cost.

Quote from @Max Bellino: I’m looking for guidance on whether it’s worth opting for a rapid report for a cost segregation study, which is less expensive than a full site visit.

Congrats on the volume!

It's a dishonest promise.If you are in foreclosure, it sounds like you are either there or headed that way,  what you are encountering is a "foreclosure scheme" they are illegal in most places and for good reason.

If they are available online or in person.