Look for people that have owned for over 10 years, and get it from them off market even at a deep discount and do the work of fixing it up and renting it for higher, or if you want to buy on market I'd definitely recommend offering below asking, as most multifamily that hits the market in these areas are tremendously over priced. 

Would you consider it a red flag if some GPs don't share their pro forma?

assuming work completes after closing.In the event of an audit, is it a red flag if we claim an "improvement" after the closing date occurred?   

I'm very intrigued by a property that is in a great neighborhood and will appreciate very strongly, but using any sort of financing on it the cash flow return is deep in the negatives for a couple years even though the ask price looks like a good deal compared to other houses around.

Do agree on the red flags part.

This is also a red tagged code violation in almost all cities. 

If a lender is not adhering to this common safeguards then that would be my first red signal .

And is walking into a turnkey ready to rock building, the seller (whom I am presuming is now broke, but that may not be the case) even left the tables and chairs behind, all ready to have plates full of unethical inorganic genetically modified red meat dipped in butter placed on them. 

Red flags all over!  

Maybe paint all the doors a deep grey or black for example, and the uppers white, then match all the hardware.