(Foundation, etc)4) Black mold, asbestos, lead paint, other other costly repairs. 5) It need significant cosmetic repairs where the purchase price just isn't worth it. 6) They may have an odd layout of the rooms. 7) Non-compliant septic.8) Trouble with permits or tenants9) Listing agent has a poor or incorrect listing.

Make sure you do an OPRA request to check for open permits and confirm with the town whether the 2/1 below is legal and permitted.

Duplex have different zoning that may permit additional units.

Supplement this far simpler entity approach by ensuring you have appropriate types and levels of insurance, you operate your business in a manner in which your conduct is not considered an exclusion in your policy, you work with licensed and insured vendors, you execute contracts with indemnification clauses with these same vendors/ require additional insured status &  maintain appropriate licensing and permits.

I expect you will need a permit and not be issued one. 

.- Does the condo have an existing STVR permit or will you need to apply for it?

You’ll want to check if your specific work falls under their home improvement contractor licensing, or if there are additional local permits required depending on the county.

You must get a permit, drill holes in the bottom, demo the bondbeam down a foot or so, and then fill with compaction inspections along the way..... last time I checked it was about $10,000

I am currently going through business permit

Assessments in NJ are not done on sale, unless it's a new build or a complete renovation where the permits tip them to reassess, so every three years or so they reassess all of the properties and taxes go up most of the time.