Tree care should be left to professionals. Most "real" tree experts have a combination of college coursework, field training and continuing education. I collected this from some different websites and added my own views.
1. Routinely pruning is a Good Idea. Pruning your trees every three to five years is not always necessary, but it is a good idea to prune a tree with dead wood — especially when the dead branches are more than two inches in diameter.
2. Mushrooms on the tree or in the lawn near the tree? If you see mushrooms or other fungi growing on your tree, or if a big limb breaks off during a storm, have an arborist out for a tree inspection before it’s too late. Those can both be signs of a bigger problem.
3. Certification? Ask your “tree expert” if he or she is certified. Ideally, you want someone who’s a member of the American Society of Consulting Arborists, the International Society of Arboriculture, the Tree Care Industry Association, or your local/state arborists’ association.
4. Think of the Three Little Pigs; The fastest growing house was the easiest to knock down. Trees advertised as fast-growing typically are weak-wooded and decay-prone, and they often have limbs that break off easily in wind and ice.
5. No Topping, EVER! If someone offers to “top” your tree to make it safer, kick him off your property. Topping was accepted 45 years ago, but science has since shown that’s the worst thing you can do to a tree. Another bad sign: someone who wants to sell you fertilizer without testing your soil first.
6. Spikes are for Telephone Poles! Never hire an arborist who uses any kind of climbing spikes, unless he’s taking the tree down. Every time he takes a step, he’s making another wound in the tree and creating a decay pocket.
7. Mulch Volcano is bad. If you pile mulch up against the trunk of the tree (we call that a mulch volcano), the moisture can’t escape, and the trunk and root can rot more easily. Make sure there’s a mulch-free doughnut shape around the base.