When I first started doing lending in Detroit.. this was an issue ... my client a big time flipper rehabber always had retired cops there with a clip board to check in the workers.. it was determined early on that much of the theft came from the exact guys that put the stuff in during the day.. they had the codes they knew what was there they would come in at night and steal it .the day cop and clip board put that to bed.So I agree with @Bryan Bannach  hire a retired policemen have him there during construction hours its the cost of owing property in the hood.. nothing unique about this.or just sell the property and buy something else.. but I think your looking to assemble so I know you probably don't want to sell.so just as stated hire security and I really like the idea of the @Patrick Liska  Cinder block fence I would for sure do that.. then put broken bottles in the concrete on top..

I live and work downtown and am on the board of San Diego downtown partnership, gentrification is a slow moving ship but it is happening.

They would only be willing to do that if I provided some sort of letter or acknowledgement of intent from the city saying the city is on board with the rezoning.

Your buyer, C, has their financing lined up by a bank ready to fund.Once C's bank has provided their funds (that's the key), your transactional lender funds your purchase of the property from A.

Check on Loopnet in your area to see if the price is inline with what others are asking for the same class, per foot, NNN or not, etc.It's definitely harder than a SFR but doable.Send off an email blast to 5-10 long time commercial agents/brokers in the area and ask their opinion on what it should rent for and see if several of them key in on the same close range.

@Ben Toth, It all depends on the niche you are choosing to pursue.For wholesaling: Big Buks for Junk Houses by Randy Phillips & If you cant wholesale after this I have nothing for you by Todd FlemingLease Options: Turn Key Investing with lease options by Matthew ChanOwner Financing: My Life & 1,000 Houses: The Art of Owner Financing by Mitch StephensGeneral: The Millionaire Real Estate Investor By Gary KellerThese books along with several others give you an idea of what is possible.

As for the keys, why did you leave the closing without getting them, if that was in the contract?

The major key to the success of investing in single family rental property is do your homework in advance and consider all the above and you'll do great . 

Basically the textbook stated that, there is a new law in New Jersey, that if you try to sell a co-op, for the same amount or less then your investment, but aren’t successful after 4+ months on the market, then you can rent it out, regardless of any lease bylaws the board of that co-op has for renting. 

The key here is that she is pregnant and due around October.