The International Society of Arboriculture (ISA) employs rigorous testing and continuing education to get and maintain certification. Consequently, certified arborists are more up-to-date on the latest science and techniques. You can ask to see their certification card, or check them out online at the ISA website.
If they truly care about trees, a tree care company will strive to take care of them right. Environmentally-friendly, organic products will help protect your trees and the surrounding flora, as well as avoiding poisoning groundwater supplies. Sustainable tree care practices can help keep your trees healthy for years to come.