How do I handle any damage when returning the current security deposit?

Based off my experience working turnover at a large apartment complex, we assessed cleaning damages two ways.

Network....find out who some of your biggest cashbuyers are in your area by going to meetups.......they also have to respect the game.2. emphasize the infestation and how much damage it has caused and let them know that its costly to fix......just make it seems worse than it really is

It is $10 per booking to insure against $500-$5M in accidental or intentional guest damages.  

We require our tenants to get renters insurance - to make sure any damage on the inside is covered.

Your city should have enforcement rules that require him to maintain his property in a manner that prevents damage to your property.If the city doesn't help, then you can try paying for it yourself and sending him the bill.

But, if there’s a roof, bad plumbing, electric, water damage mold, if there’s multiple BIG issues, it’s a no go as it will not be cheap.

(Broken windows, heater broken, leaking water pipes, electrical problems, holes in walls, rotting porch, among other damages.)The buyer continues to make payments, but if they stop then you have a ton of repairs before you can rent out the house.

If work needs to be done to mitigate long term damage, can he say no to it being done?

I never checked that room, so the damage was there probably before their lease started.