One of the most likely places for mold to form is anywhere that moisture is improperly vented. Another area of concern is if a home has ever flooded and was not absolutely or properly cleaned and dried after. Leaky plumbing and basement crawlspaces are other likely candidates. Mold can be a difficult thing to absolutely get rid of as the only thing it needs to continue growth is an organic material such as wood, and moisture. Both of these items are usually abundant in any home. The most likely was that moisture finds its way into the home is through faulty or leaky roofs and foundations. Both of these areas should be checked over by an experienced mold inspector on a evenhandedly regular basis if there is any worry of mold beginning to grow, or if these has been mold in the past. Mold can be an costly problem to deal with so be pro-active about looking for it, it can save you money in the long run.