Even in that case, we are bound to make mistake so I would rather learn here on BP and network and get help from amazing people in BP community here.     

Seller will loose the construction money he/she put into the property

But with no documentation you may loose.

This is what was inside -- over 100 boxes of ammo (all sizes), not including the 1000 or so loose rounds and clips.

The tenant only has the choice of buying the home at the agreed at price of the option contract or loose his money at the end of the contract.The rent is a separate issue as you mentioned.

If i loose too much I'll stop doing it.

I won't let myself loose that money I rather not make money then loose money.

You are right about the investor loosing money. 

Another option would be to put down a huge EMD and remove your finance contigency, but make sure you are getting that loan or you'll loose the huge EMD!  

Everything is negotiable and from the banks perspective there are costs to not selling; holding costs, opportunity costs, re-listing costs, etc. and simple aggravation.Even if they have a specific price below which they 'say' they will not sell, ask yourself if they would not accept that price less $1.The art of negotiation is always a challenge.On the other hand, if you really believe that it is a good deal at the price it is now being offered at, are you willing to risk loosing it.I would come in something below their current ask.