There is surface and airbrone mold so even if you demo the problem and don't irradicate the source it can come back.In other wors you replace everything where the mold is you don't fix the source and put new everything in there buyer buys house mold occurs and they sue.
When I offer to purchase a house with mold I pay ALOT less than a regular flip simply because of the stigma attatched even when getting a clearance certificate from a mold remediation company.
Make sure on your next purchase you know more about disclosure and the difference between mold and mildew.If you go to
http://www.epa.gov you can get a ton of free info.