Then move from there.It's free for a reason: falling apart, bugs and pests inhabit, mold and other toxins, unsafe (condemnable) habitation, etc.

There are very few exceptions such as for products that are harmful to children (cigarettes, alcohol etc.).

My only obligation to them was to get my property back in working order and be deemed habitable by the local fire marshal. 

and you should be able to report their payment habits to a credit bureau.So, if you have  tenant wanting the place, I would collect the late fee, let them move out and deduct anything past normal wear and tear and return the deposit quickly.  

Do not let them make this a habit.

Is this a property that is or was recently habited or the seller was paying a mortagage on an uninhabitable property?

After that they will have trouble suing since as a landlord you have a duty to provide a habitable residence and you performed your duty by looking into the issue and cleaned it up once aware of the issue.

If you tell her your max, the owners know exactly what you are willing to pay and you lose your negotiating leverage.Using a buyers agent is 100% FREE to you as the seller pays the agent's fees, so there is no harm.

I have owners that fix everything and owners that I must fight with to keep the homes in habitable condition.

I have owners that fix everything and owners that I must fight with to keep the homes in habitable condition.