Most molds are of the non-toxic variety. You can ignore it if doesn't affect the value of the property but always listen to experts before making the ultimate decision because a mold can cause unpleasant smell and health problems in the future. You have to decide whether fixing the issue is worth the price you will pay. As the seller couldn't fix the problem if you are interested enough to buy the home, you can ask the seller to reduce the price. If you still want an expert advice, contact link removed.