There are a few basics to look for when evaluating tree health. First check for dead trees, these can fall and damage property. Next look for large dead branches in trees; this can be a sign of stress or decline in tree health. Beyond these two basic conditions tree health should be evaluated by a professional. A Certified Arborist has training in detection of tree defects. Some trees appear perfectly healthy but could be full of decay. This decay could be hard to detect especially in roots. Decay is the number one defect causing tree failure. A tree risk evaluation can be done for any or all of your trees in question. Expect to pay a fee for this service. Trees greatly increase real estate values and buying property with mature trees will be worth the investment as long as the trees are in good condition.