I would be very surprised if you can find something with two legitimate dwellings in an A or B neighborhood for less. 

What specific document would be needed to show that they are legitimate heirs and to express interest in selling?

Is this legitimate?

It kinda like the old adage “ do as I say not what I do”. earnest deposit are comforting as well legitimate.

@Matt Snow Wow, someone after all this time finally answered my question in full detail with not only legitimate responses but intelligent ones which are cited sources.

Do I possibly lose a legitimate client here and there because of that?

If, however, there are no finance or inspection contingencies (often the case with wholesaling) then there are few legitimate reasons not to close; certainly a lot less reasons than a standard MLS purchase that typically states financial and inspection contingencies.  

Would you say taking into account my market's trends when it comes to rising rents, property values, and moving trends is pure speculation or a legitimate investment analysis?

The seller had a legitimate reason for wanting to close that fast.... she was adopting a child and needed the money quickly to facilitate that.

You may have a legitimate reason to do so like great cash flow.