I'm about the clean it up and put some anti mold primer on it.I need to have an mold inspector certify it.

Do I even consider giving their deposit back if it's clean?

SLO and ST are best (and should only be used) on clean properties...with clean title. 

This new bookkeeper seems to be the cream of the crop and I'm paying $500 per month plus 2k set up fee (After having paid my last bookkeeper 4k to clean up my books) (my point is... am I spending enough that they should have a fix for me or can I not rely on that?) 

Is there a letter or cleaning list you send to the tenant addressing what would need done before they leave?

Honestly, with COVID here and so many people not working; if someone that has a clean background and has a job moves in with a current tenant, it just gives more financial stability to the unit.

I am personally using the opportunity cost as a benchmark for my decision making; how much will it cost in terms of missed rent, costs to clean and market the property vs how much will I lose is I let a few months slide.

How about cleaning the unit/house with a hospital disinfectant? 

lawn mowers & cleaning people still tuff. 

That means gutters, clean gutters, drainage pipe leading away from the house, base pitching away from the house, etc.