The counties I am most familiar with, Franklin (Columbus) and those counties that surround Franklin, have zoning laws and land use codes and, if the property is in a subdivision, many of those have restrictions as well.Find some Columbus SF addresses on Zillow and look them up on the Franklin County Auditor website. 

@Dave Dunaway as long as the units meet code, you're good...we just passed on 8 duplexes where the design called for basement apartments...typically, below grade footage carries less value than above grade...so, for example...if the upstairs is $100/sq.ft. you won't double your square footage at the same rate by putting living space in the basement....and you are basically asking the auditor to reassess your taxes based on the square footage...so you claim it...you pay taxes on it.Most of the other inherent issues are around controlling water...the right thing to do would be to install a perimeter drain and sump...if there is any moisture or water intrusion in the basement (and there will be), you run the risk of mold inside the finished walls...I think my ultimate questions is who would really want to rent an apartment with the bedroom in the basement...even if it is finished, but who knows.

I currently work as a full time auditor, and was hoping that I can put in extra hours each week to try to even close one deal, but as you said, it would be a full-time job itself.

I think we’ve been leaving money on the table for YEARS since his dad, who retired from the Ohio State Auditors office, has been preparing our taxes.  

. :)What these accountants seem to rely on is the combination of a very low probability of an audit to begin with, and then an even lower probability of an auditor raising the land allocation issue, and then an almost zero probability of the auditor trained well enough to contest it.So you will probably get away with 80/20, but it still does not make it right.

The county auditor website where we invest allows you to screen for 4-19 units in different neighborhoods so we could put together a pretty targeted list. 

These are the compliance auditors and examiners for institutions generally, this is still a gray area as you may have a small bank officer who has had to self-study through this maze , then you may have a compliance officer from a large institution who has attended formal training, so consider that. 

I've had an auditor argue for 2 hours over $48 in tolls at the 25% bracket.

Would being an auditor for real estate companies be beneficial to starting real estate investing and learning the basics?

There are firms that specialize in small corps about to become public for SEC audits, there are firms that audit HOAs, and on and on...Alsi most furms, it is actually a staff auditor that may or may not have their CPA licensure that actually performs the audit.