IF the sellers knew, or reasonably must have known (logically, under the circumstances, must have known) about the mold but nonetheless failed to disclose it, they may have committed fraud. If you have a contractor (the Servpro employee) who can, if necessary, testify that he told the owners that there was mold, then it is very likely that you can establish their knowledge. In that case, you could sue the sellers--unfortunately, if they will not voluntarily compensate you, the only way to get compenation is via a lawsuit--for the cost to remediate or correct the problem (i.e. to get rid of the mold and fix any damage done in the process).