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. Tree care requires experience, education and skill, therefore professionals should be carefully selected. A phone ad is no guarantee of good work, but at least indicates some degree of permanence. Beware of doorknockers.
Most reputable companies have plenty of work without door knocking.
Doorknockers 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.