If they are not kept sealed then they will stain.  

Mold remediation is remove everything you can, spray with killer, seal with an encapsulant.

The front left is crappy you need to seal it.

We sealed it every 6 months or so and never had any staining or issues.

And my all-time favorite for the kitchen, if the cabinet boxes are good, have them painted (make sure to seal the paint with a good dewaxed shellac or polyurethane) and fit new door and drawer hardware for buck or two apiece. 

It needs to be sealed about once a year. 

I will have it cleaned and sealed.  

It was not an easy one, since we are in CA and the property is in OH, but we made it through and are looking to take on our next project.Bought: $79,900Initial budget: $65,000Real budget: $97,000 (mismanaged project by initial contractor (and second contractor))ARV: $219,900Improvements:Brand new siding on the second floor (was not in the initial budget)New roof (was not in the initial budget)Sealed and painted the basement - was quite creepy down there beforeOpened the floor plan from the living to the kitchen by widening an existing walkwayMoved the kitchen from one side of the house to the other to capitalize on the stained glass windowsGutted the upstairs bathroom and added really good looking featuresAdded a half bathroom and laundry room downstairs by the entry to the backyardNew ACNew plumbingNew electricOur contractor performed extremely poorly on this job, and I am happy to share a cautious word with anyone who aims to invest in Cincinnati about the team at Kaiker Development and Creative Customs Carpentry.

We finally sealed all the walls, ceilings and floors with Zessner odor killing sealer which helped a lot, purchased an air purifier, and kept the house open as much as we could. 

@Dillon Seal yes it is certainly legal but the lender has to comply with much more strict rules if you are going to live there.