Look for an arborist. An arborist will offer a higher level of service than someone with a chainsaw who simply cuts down trees. Arborists can be found in the phonebook or through simple Internet searches.
Call your local city hall. Many municipalities require licensing for arborists. Ask to speak to the person in charge of hiring tree service professionals for your municipality. Find out what tree service companies your local government uses. Call these companies and ask if they provide the type of service you need. Inquire about their professional affiliations and licenses and ask if they can provide references from satisfied customers.
Visit or contact your local chamber of commerce. Ask for information about any member businesses who provide tree services and check their credentials.
Call your power company if the reason you're seeking a tree service involves power line issues. Depending on the location of a tree or trees, the power company may take responsibility for maintenance procedures if power lines are affected.
Shop for a tree service during the off-season to save money. The best tree service providers are often booked solid during the summer months. Many will offer discounts for winter work.
Avoid problems by asking to see proof of insurance, current certificates of liability and workers compensation insurance before any work begins.