Are you claiming that the client was harmed because they received more money? 

If you are worried more about "should I do this because I don't want to harm my condensing unit" then an easier source of information is your manufacturer's recommendations, which may be listed online or available for download.If you are worried more about "I want to do it regardless of performance issues but just need to know if I am allowed" then a quick phone call to the code enforcement office Monday or Tuesday (whenever they decide to open) will be better than anything anyone here can tell you (unless, of course, someone in DeKalb County had the same issue they researched).When you call, all you need to do is ask to speak with code enforcement and then ask: "When it comes to building a deck, are there any rules about required clearances above air conditioner condensing units?"

A 30 year old HVAC system probably uses the "old" freon, which costs so much more due to government/environmental regulations put in place due to its harmfulness to the planet.

The other harm is that your IRA (your retirement) grows at a smaller rate since you depleted it.

What happens if they harm one of my tenants kids sexually or something?

There's no harm in making a few calls before you retain someone if you intend to do a lot of business with them. 

I get concerned about attracting vermin, neighbor complaints, pulling the neighborhood down, harming the bones of the property, and hoarding.  

If you sign a deal that is not really a deal hoping to lie your way to getting a buyer it won't work and you will have to back out, going back on your word to the seller and harming your reputation.

The amount this harms you doesn't make them a less bad or more bad person. 

I don't see the harm of using a new agent if you have others to help you with strategy and evaluation.