(That has never been an issue for me but that is something you want if you are going to spend the money on the report - the engineer is responsible if the repairs fail per their recommendation, not you)  

What are the bare minimum requirements I should request in a written agreement/legal document with this individual to best protect my asset in case his investment fails or falls short.

I am new to real estate, and though there is loads of amazing information here on how to succeed, I am looking for more information on how to fail (Not that I intend to!).

The seller also had 2 failed sales within the last year at $530k and $540K, respectively.

I used to dive into conversations like this, but I gave up “forecasting” years ago after my crystal ball had failed me so many times.

I have been reading on the subject matter and failed to see this point.

If you don't find a property in time, the exchange just fails and you simply pay the taxes.

I failed to mention the property is located in Washington state, although I am based in Los Angeles.

If they fail to do so, then dispose of it and bill them as Matthew Paul suggested.  

These products usually move a little more slowly than a fixed asset so they can be great fail safe identifications for a 45 day identification list.The biggest obstacles to these in general are unrealistic investor expectation of return in the wholely owned sector.