The airport had the buildings (from when federal gov turned the land over to the Airport Authority after WW2.) and allowed the current "owner" to spend a few $M improving the buildings.

With some of my clients, I've seen discounts of 30% to 90%.Here is a real-life example: I invested in a $50K note; it was second TD but with significant equity (over $200K) protecting my investment. 

what kind of investment was/is this  a little more detail may protect others if you think this person is a financial predator.  

I don't get that much business from BP but when I do the transaction values are big enough to justify all of the time that I spend on here.

Do not spend profits (or pay yourself) for atleast 6 months.

I'd spend maybe ~$60k of that money.

How can I best protect the seller as well as myself?

Just my thought is the closer you get to nyc the more you’ll have to spend

If you added in the cash you should have to protect against contingencies, the actual return goes down (or the risk sykrockets, your choice)- If the $300K properties cashflow, definitely a better bet. 

Once they cut the govt spending that is going to equate to negative job growth most likely for periods of time.