There is a big distinction between a "tree guy" and a certified arborist. While an arborist is defined as someone who specializes in the care of trees, a certified arborist has proven his/her knowledge in the art and science of tree care by passing an exam, administered by a state organization and/or the International Society of Arboriculture (ISA). Once certified, the arborist must maintain their credentials by obtaining continuing education credits, attending conferences, seminars and other educational events. Because of these requirements, certified arborists will be the most up to date on the latest technology and information available in the proper care of trees and shrubs.
Look closely at this tree that was "pruned" by a tree guy: