The difference between a Certified Arborist and a Consulting Arborist resides with the organization that issues the title.
Certified Arborists are accredited through the International Society of Arboriculture (ISA). Each individual who passes the specific test for certification will hold the title of 'Certified Arborist' for three years, during which time they must accumulate 30 continuing education units to maintain their certification. In general, Certified Arborists work for a company that offers a variety of tree care services, such as pruning, fertilization, cabling, lightning protection, pest management, etc.
The title Consulting Arborist, or more correctly, Registered Consulting Arborist, is issued through the American Society of Consulting Arborists. These individuals must meet the requirements of this organization to retain their title. In general, Consulting Arborists offer services that result in detailed reports to homeowners and clients regarding tree protection, risk assessments and value appraisals. A Consulting Arborist may also be more likely to be called as an expert witness in legal situations.
Read more in the article, Arborists: Selection & Services