The internet has changed almost everything. One thing that it has not changed is that references from trusted friends and associates are the best source for referrals.
The professional web based listing services are in business to make money, not do a free service. They make money from the advertising dollars of the listed professionals. In some of these listings there is a review of the contractor’s reputation, in others “not so much.” Position on almost all of the sites is dependent upon advertising payment. Understand that the first company may be the worst on the list.
If using a list on the internet, check the company for certifications. Then check the certifying agency to make sure they actually have the certification. Check the PA State Attorney website. In a high portion of consumer complaints, the contractors provided a contractor’s license number that was a fake or expired.