Imagine a surgeon having to work with a chainsaw while balancing on a tree limb while trying not to fall off the operating table. Trees need to be pruned to improve tree health, for public and private safety and to maintain power lines. Homeowners should know proper pruning techniques and they should only prune limbs they can reach while standing on the ground. A phone ad is no guarantee of good work, but at least indicates some degree of permanence. Beware of door knockers.
Most reputable companies have plenty of work without door knocking.
Door knockers are especially common after a storm. Never let yourself be rushed by bargains. Then phone the insurance company to make certain the policy is current. Ask for local references. Ask neighbors and friends if they have used an arborist.