I noticed a concrete slab about 150 feet from the main house.   

I do everything from the road to the concrete slab (minus drilling wells).

@Jonathan R McLaughlin hit the correct answer (at least the one I have run into before).It can be a pain because use has to pre-date when the zoning made it non-compliant.

I tried to put that language in the original contract but then the seller said “we need something concrete, before we move forward”

The tiles adjacent to the wall and the baseboard have been removed, the drain tile put in, concreted over, and this has left a depressed section 18”wide that has a drop off of ¼” from the existing tile.For a quick, low-cost solution, I was thinking of putting floor leveler in, then painting it a similar color to the tile that’s there, then putting the baseboard.

Bear that in mind Also, they hid some damage under concrete and didn't disclose it ( why would they care) 

It's compliant with the law. 

Main items of concern:Lease set up: Business to owner, specific items to include - boiler plate or company that can generate for a feeLiability issues and insuranceADA requirements: the owner had stated only required depending on what tenants live in the facility- carbon/smoke alarms - no ramps, etc (seems fishy as in construction rules on ADA are stringent)As the owner do I need any short of license?

This was based on case law of lawsuits filed by both private parties and the SEC, and judicial decisions and court rulings in various district courts.To make things more concrete for private issuers, the SEC instituted “safe harbor” rules centered around Regulation D section 504, 505 and 506.

The contractor did some concrete stains on the tenant's rug.The tenant is asking me to refund her the rug.