Legal contractors are licensed by the State, carry liability insurance and are bonded.
Any advertising requires listing of the contractor number. The State website has a contractor lookup. It's pretty easy to see if there are any complaints, whether they are insured or not.
Tradesmen like plumbers and electricians are licensed, pull permits and get inspections.
A licensed contractor is certainly more likely to have more practical experience and apt to know the correct procedures. They're not guessing.
There's no recourse using non-licensed workers. They insurance companies don't back their work.