I wouldn't raze rent,  unless you have money to burn. 

A week later, someone purchased the property for 10k more then I had offered, in cash.Since that burn, real estate's had a special place for me.

I understand if it burns down, I am out on my duplex, but it will have good cash flow until it does.My question... how much of a percentage do I take off from the comps because it's zoned single?

Some say I am being vindictive; I feel I am doing all a favor by  bringing the facts to light so that the next landlord wont get 'burned" by a rotten apple.What are others views on this?

If this was one of my properties  they could walk out or they would be carried out.Take all their stuff out right in front of them and burn it all in the front yard. 

-Does the property have/plan on having any of the following: electric space heater, kerosene heater, wood burning stove?

The agent did say that they would require I sign an exclusive agent agreement ( with no penalty for cancelling agreement) in order for them to work with me as they have been burned by previous investors.I have another question.

I will not live under someone's thumb, but I've grown up enough to not burn the bridges too badly.  

I know it's already happened and you unfortunately got burned by this bad tenant but the big "no-no" was to let her receive services under your name. 

People have made millions by making the right guess (look at brooklyn or hoboken), and people have also been burned by making the wrong guess.