It addressed hardening the rental.

@Jason Anderson while I fully agree with @Nathan Harden's comment on youtube being a great resource. 

Sealing the basement floor might help   (something that soaks into concrete then hardens,   as oppposed to a paint which sits on surface and flakes off)  then clean the carpets,  there may have been dirty spots providing nutrients to the mold.Add a basement ventilation fan that runs on a timer or continously to keep humidity down.   

The book has many great tips on how to harden/optimize your property for section 8, how to pass the inspection, deal with section 8 and screening tenants.

I've been burned more than I want to admit, and hardened.

So for example I'm very conservative and don't want any debt on them because I feel this hardens them in case of a severe recession.

I usually only "harden" them to get them ready for the abuse they're about to endure and also do roofs, exterior paint, new HVACs, etc.

But lately, we’ve become a lot more discerning (maybe “battle-hardened” is a better word?)

After the concrete cured/hardened there were no further problems, but the cost was not cheap and the results are not warranted.

So for example I'm very conservative and don't want any debt on them because I feel this hardens them in case of a severe recession.