Being a member of this site and using some or all its will make your journey to success faster and less bumpy.  

If there's some way to compel the Seller to give you what you need to make you whole, whether it's access-- or an Easement-- or a boundary line adjustment around structure-- or a boundary line adjustment around structure PLUS setback--  and/or all of the aforementioned plus enough land to make it a legal lot on its own (e.g., if the acreage is shy from the zoning requirement in the neighborhood,) then a good lawyer will know it.  

In my opinion, the previous unit owner was extremely negligent in not stopping, &/or reporting some or all of these problems.

If any, or all of those, break would you be able to fix it? 

Did the guru mean purchase price at 75% ARV or all-in (including rehab and financing/closing) at 75% of ARV?  

Creating a note and selling them for a part of it or all of it has been around a long timeStudy simultaneous financing with notes@Marc Faulkner

The buyer probably brought kids to our house and they left pop corn residuals on the floor, stairs and master bathroom.We were so shocked, so we filed oral complaints right away.

Well there's nothing legally holding you back from calling them and telling them the rent will be higher, although some or all of them may not want the place at the higher rent.

It applies to individual duplexes or all together.  

Some or all of the closing cost can be negotiated from the seller.