For the overboard I will probably poke holes until the joists are revealed to nail the new boards. 

A web search should reveal most of them.

The Home Inspector report revealed major deficiencies in the rehab and the Home Inspector told me that the rehab was like “putting lipstick on a pig”.

That's a solid approach for dealing with your own tenant.Do not, of course, reveal your information source, but give them the option of being investigated or leaving. 

I have an SFR in Memphis that I purchased a couple of years ago for $60k (Original contract was for $70k but inspection revealed a need for a new roof so I asked for $10k off).  

However, I suggest you don't reveal you know how much is owed in taxes.

Another gentleman was working within, and a conversation with him revealed the owner, that he was getting ready to sell the house and how much he wanted for it.I knew the numbers for my neighborhood, and immediately knew that this was a profitable scenario.

Perhaps your agent revealed it.If the home is properly priced for its condition, your agent needs to give you a LOT better advice.  

If they show rental, royalty, or dividend income, but the assets/liabilities sheet does not reveal any rental real estate, oil and gas interests, or stocks/bonds, then the negotiator will think they are being scammed.

This can be a good or a bad thing depending on the short and long term socioeconomics and demographics of the area.If it's currently zoned as a MHP and your due diligence reveals that it's in the path of progress and the infrastructure isn't in too bad of shape then it might be worth pursuing.