Mold is a red flag for many buyers; I would suggest the flag should be yellow. I have posted an article from the Washington Post which posits that mold may be “an opportunity to snag a good house for a discount.” Rather than panicking, a savvy buyer should get a better understanding of the nature and extent of the mold issue and work with their real estate professionals to find a solution.
The EPA’s Brief Guide to Mold is a good starting point for better understanding the cause and dangers of mold. Both the EPA and the Illinois Department of Public Health emphasize first identifying and correcting the source of the moisture causing the mold and then cleaning or removing the mold. If the moldy area is less than about 10 square feet (less than roughly a 3 ft. by 3 ft. patch), in most cases, you can handle the job yourself. However, if there has been a lot of water damage, and/or mold growth covers more than 10 square feet, a mold remediation company should be brought in correct the problem.
Nonetheless, The Illinois Department of Public Health does not recommend mold testing. They point out that unlike Radon for example, no standards or guidelines exist to judge acceptable amounts of mold. They also note that Mold testing is not typically useful in determining what steps to take for cleanup.