I had a thorough inspection of all the houses we considered buying done. If anything was wrong we moved on. condensation and mold formation in AC/HC ducting is a serious problem. Also if you are not on a slab.. mold in a conventional foundation or basement can give you serious trouble. There are epoxy sealants for basements and crawls spaces that can help.. cleaning ducting is alot more grueling.

Best of luck with it.
MG